The 77-year-old emperor expressed his own deep concern about the "unpredictable" nuclear crisis. "With the help of those involved I hope things will not get worse," he said.
U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko said at a congressional hearing in Washington that all the water is gone from the spent fuel storage pond of Fukushima Dai-ichi's Unit 4 reactor, but Japanese officials denied it. Hajime Motojuku, a spokesman for plant operator Tokyo Electric Power Co., said the "condition is stable" at Unit 4.
Earlier, however, another utility spokesman said officials' greatest concerns were the spent fuel pools, which lack the protective shells that reactors have.
"We haven't been able to get any of the latest data at any spent fuel pools. We don't have the latest water levels, temperatures, none of the latest information for any of the four reactors," Masahisa Otsuki said.
If Jaczko is correct, it would mean there's nothing to stop the used fuel rods from getting hotter and ultimately melting down. The outer shells of the rods could also ignite with enough force to propel the radioactive fuel inside over a wide area.
"My understanding is there is no water in the spent fuel pool," Jaczko told reporters after the hearing. "I hope my information is wrong. It's a terrible tragedy for Japan."
He said the information was coming from NRC staff in Tokyo who are working with the utility in Japan. He said the staffers continue to believe the spent fuel pool is dry.
Other countries have complained that Japan has been too slow and vague in releasing details about its rapidly evolving crisis at complex of six reactors along Japan's northeastern coast, which was ravaged by Friday's magnitude-9.0 earthquake and subsequent tsunami.
The chief of the U.N. nuclear agency, Yukiya Amano, said he would go to Japan to assess what he called a "very serious" situation and urged Tokyo to provide better information to his organization.
Several countries have advised their citizens to consider leaving Tokyo and earthquake-affected areas. The White House recommended Wednesday that U.S. citizens stay 50 miles (80 kilometers) away from the Fukushima Dai-ichi plant, not the 20-mile (32-kilometer) radius recommended by the Japanese government.
Japanese officials raised hopes of easing the crisis, saying early Thursday that they may be close to bringing power back to the plant and restoring the reactors' cooling systems. The earthquake and tsunami knocked out power and ruined backup generators.
The new power line would revive electric-powered pumps, allowing the company to control the rising temperatures and pressure that have led to at least partial meltdowns in three reactors. The company is also trying to repair its existing disabled power line.
Tokyo Electric Power spokesman Naoki Tsunoda said the new power line to the Fukushima Dai-ichi plant is almost finished and that officials plan to try it "as soon as possible," but he could not say exactly when.
Conditions at the plant appeared to worsen, meanwhile. A surge in radiation levels forced workers to retreat for hours Wednesday, costing them valuable time.
The radiation spike was believed to have come from Unit 3, but officials acknowledged they were far from sure what was going on there or at other troubled reactors, in part because high radiation levels made it difficult to get very close.
About 180 emergency workers have been working in shifts to manually pump seawater into the overheating reactors to cool them and stave off complete meltdowns. They were emerging as heroes as their sacrifices became clearer, and as they stepped into circumstances in which no radiation suit could completely protect them.
Japan's health ministry made what it described as an "unavoidable" change Wednesday, more than doubling the amount of radiation to which the workers can be legally exposed.
"I don't know any other way to say it, but this is like suicide fighters in a war," said Keiichi Nakagawa, associate professor of the Department of Radiology at the University of Tokyo Hospital.
Late Wednesday, government officials said they asked special police units to bring in water cannons normally used to quell rioters to spray water onto the spent fuel storage pool at Unit 4. The cannons are thought to be strong enough to allow emergency workers to remain a safe distance from the complex, said Minoru Ogoda of Japan's nuclear safety agency.
Tokyo Electric Power said it was also considering using military helicopters to douse the reactors with water, after giving up on such a plan because of high radiation levels in the atmosphere.
Units 1, 2 and 3 of Fukushima Dai-ichi have all been rocked by explosions, and officials have acknowledged that their cores have begun to melt down. Compounding the problems, a fire broke out Tuesday and Wednesday in the Unit 4 fuel storage pond, causing radioactivity to be released into the atmosphere. Temperatures also have been rising in Units 5 and 6.
White smoke was seen rising Wednesday above Unit 3, but officials could not ascertain the source. They said it could be spewing from the reactor's spent fuel pool or may have been from damage to the reactor's containment vessel, a protective shell of thick concrete.
The nuclear crisis has partly overshadowed the human tragedy caused by Friday's massive earthquake, one of the strongest recorded in history.
Millions of Japanese have been with little food and water in heavy snow and rain. In some towns, long lines of cars waited outside the few open gas stations, with others lined up at rice-vending machines.
More than 4,300 people are officially listed as dead, but officials believe the toll will climb to well over 10,000. Police say more than 452,000 people are staying in temporary shelters such as school gymnasiums.
The threat of nuclear disaster only added to Japanese misery and frustration.
"The anxiety and anger being felt by people in Fukushima have reached a boiling point," the governor of Fukushima prefecture, Yuhei Sato, fumed in an interview with NHK. He criticized preparations for an evacuation if conditions worsen, and said centers do not have enough hot meals and basic necessities.
In the city of Fukushima, about 40 miles (60 kilometers) inland from the nuclear complex, hundreds of harried government workers, police officers and others struggled to stay on top of the situation in a makeshift command center.
An entire floor of one of the prefecture's office buildings had been taken over by people tracking evacuations, power needs, death tolls and food supplies.
Elevated levels of radiation were detected well outside the 20-mile (30-kilometer) emergency area around the plants. In Ibaraki prefecture, just south of Fukushima, officials said radiation levels were about 300 times normal levels by late Wednesday morning. It would take three years of constant exposure to these higher levels to raise a person's risk of cancer.
A little radiation has also been detected in Tokyo, triggering panic buying of food and water.
Given the reported radiation levels, John Price, an Australian-based nuclear safety expert, said he saw few health risks for the general public so far. But he said he was surprised by how little information the Japanese were sharing.
"We don't know even the fundamentals of what's happening, what's wrong, what isn't working. We're all guessing," he said. "I would have thought they would put on a panel of experts every two hours."
Chief Cabinet Secretary Yukio Edano said the government expects to ask the U.S. military for help, though he did not elaborate. He said the government is still considering whether to accept offers of help from other countries.
In other developments:
U.S. troops banned from area around nuclear plant • The White House is advising Americans in the area around the crippled Japanese nuclear plant to follow more stringent safety precautions than those set by the Japanese government.
The U.S. is recommending its citizens stay 50 miles away from the nuclear plant because of the risk of radiation exposure, while Japan is recommending people stay 20 miles away.
White House spokesman Jay Carney said Wednesday it was clear that the situation in Japan is "deteriorating and fast-moving." He sidestepped questions about whether the new U.S. recommendations signaled a lack of confidence in the Japanese government's handling of the crisis.
"I will not from here judge the Japanese evaluation," Carney said. "It is simply a separate analysis based on American standards."
U.S. military relief crews near the troubled Fukushima Dai-ichi facility are receiving anti-radiation pills before missions to areas of possible radiation exposure, the Pentagon said Wednesday.
More governments advising citizens to leave Tokyo • Australia and Germany advised their citizens in Japan on Wednesday to consider leaving Tokyo and earthquake-affected areas, joining a growing number of governments and businesses telling their people it may be safer elsewhere.
The advisories came as the crisis at Japan's Fukushima Dai-ichi nuclear plant in the northeast deepened in the wake of last week's earthquake and ensuing tsunami. Surging radiation forced Japan to order workers to temporarily withdraw from the plant Wednesday, a setback to efforts to cool its overheating reactors.
The Department of Foreign Affairs and Trade, however, said its advice to Australians had nothing to do with the threat of nuclear contamination from the damaged plant.
"We are providing this advice because of the continuing disruption to major infrastructure, its impact on the welfare of people on the ground and continuing aftershocks," its notice said.
Hope and loss in search for 8,000 missing • Line after line, a list on the wall of city hall reveals the dead. Some are named. Others are identified only by a short description.
Female. About 50. Peanuts in left chest pocket. Large mole. Seiko watch.
Male. 70-80 years old. Wearing an apron that says "Rentacom."
One set catches the eye of Hideki Kano, a man who appears to be in his 30s.
"I think that's my mom!" he says. He rushes out into the snow, headed for a makeshift morgue.
The list in Natori, and others along Japan's northeast coast, will only get longer.
Five days after the 9.0-magnitude earthquake and tsunami, the official death toll is more than 4,300. More than 8,000 people are still missing, and hundreds of national and international rescue teams are looking for them.
In the industrial town of Kamaishi, 70 British firefighters in bright orange uniforms clamber over piles of upturned cars to search a narrow row of pulverized homes. They wear personal radiation detectors amid fears of leaks from damaged nuclear plants far to the south.
One woman's body is found wedged beneath a refrigerator in a two-story home pushed onto its side.
"Today and tomorrow there is still hope that we will find survivors," says Pete Stevenson, head of the British rescue crews. "We'll just keep on carrying out the searches."
Those seeking loved ones have posted hopeful notes in temporary shelters and other public places. They cover the front windows of Natori City Hall, blocking the view inside:
"I'm looking for an old man, 75 years old, please call if you find him."
"Kento Shibayama is in the health center in front of the public gym."
"To Miyuki Nakayama: Everyone in your family is OK! We can't use our mobile phones, so you can't call us, but we're all here. If you can come home, please come! We're praying for you."
City officials have posted a list of 5,000 people staying at shelters. Yu Sato, 28, snapped photos of the names.
"I'll post them on the Internet so people living far away can check," he says.
In Otsuchi town, Reiko Miura conducts her own search.
She's looking for a 50-year-old nephew who couldn't flee the tsunami because of a work injury that had phyiscally disabled him. His mother Miura's sister asked her to look for her son.
But for the 68-year-old woman, it is a struggle just to recognize the neighborhood, now a sea of mud punctuated by tossed cars and mounds of debris.
"I'm pretty sure that my family home is here. It was a big house," she says upon reaching a pile of rubble in a location that feels familiar. But there's no sign of her nephew, and she trudges back across the mud, unsure what to tell her sister.
The devastation is of such magnitude that it is hard to imagine some of the communities ever being rebuilt. Town after town has been wiped away.
Each curve in the road opens onto a new scene of destruction a van balanced precariously on the railing of a Buddhist temple, a handbag inside an overturned washing machine.
Kesen is virtually a ghost town.
Miyuki Kanno, who lives a few miles (kilometers) away, rode his bicycle down a mud- and water-choked section of road looking for information about missing relatives. He guessed it would take 20 years for Kesen to come back.
"Your hometown is your hometown. They'll rebuild. I don't know if the young people will come back, but they'll rebuild," he says.
Farther north in Ofunato, 72-year-old Keiichi Nagai is less sure.
He stands on the edge of a huge wasteland that used to be the low-lying part of the city. He shakes his head and repeats, "There's nothing left, there's nothing left."
He points at a washed-up fishing boat that he said destroyed his house. All he managed to salvage was a small brown wallet with a hospital card.
"There's nothing left of this place," he says. "The population is going to be half what it was. It's scary to live here now. People will think it's dangerous. There's a chance another tsunami will come. I won't live here. Maybe on the hill but not here."
Some 430,000 people are in temporary shelters, too worried about daily survival to think of the future.
Some 350 in the gym and theater of an Ofunato middle school have fashioned beds from cardboard mats and blankets. Elderly residents huddle around gas heaters, and youths kick a soccer ball on a snow-laced baseball field.
Japanese military officers stock vats of water in a parking lot and ferry in bananas, rice balls and miso paste.
In Kesennuma, another coastal city, Kayoko Watabe arrives at a shelter after trudging through mud and thick snow. The 58-year-old woman is wearing the same clothes she had on when the tsunami struck.
She is staying with relatives who lack electricity, heat and water, and she's come to the shelter a junior high school to get food and other necessities. There, she finds survivors living in classrooms. Most lie on the floor, wrapped in blankets. The stench of unflushed urinals fills the hallway.
"We've never seen or experienced suffering like this," she says. "All I can think about is where to get food and stay warm."
Associated Press writers Jay Alabaster, Foster Klug, David Stringer, Koji Ueda, Eric Talmadge in Fukushima, Elaine Kurtenbach and Shino Yuasa in Tokyo, David Stringer in Ofunato and Jocelyn Gecker in Bangkok contributed to this report.