In June, ethnic violence in the state left at least 90 people dead and destroyed more than 3,000 homes. Tens of thousands of people remain in refugee camps.
The United States called for Myanmar authorities to take immediate action to halt the violence. The United Nations appealed for calm.
An Associated Press photographer who traveled to Kyauktaw, one of the affected townships 45 kilometers (75 miles) north of the Rakhine capital of Sittwe, said he saw 11 wounded people brought by ambulance to the local 25-bed hospital, most with gunshot wounds.
One was declared dead after arrival. All the victims being treated were Rakhine, but that could reflect an inability or unwillingness of Rohingya victims to be treated there.
A male volunteer at the hospital, Min Oo, said by telephone that five bodies, including one of a woman, had also been brought there. He said the injured persons were brought by boat from Kyauktaw town 16 kilometers (10 miles) away, and taken from the jetty by the ambulances.
An account by a Rakhine villager in the area suggested great confusion and tension. The villager said that when groups of Rakhine and the Rohingya had a confrontation, government soldiers shot into a crowd of Rakhine, even though, according to his claim, it had been dispersing. The villager would not give his name for fear of violent reprisals.
There have been concerns in the past that soldiers were failing to protect the Rohingya community, but the Rakhine villager's account hints that the military may have been defending the Rohingya in this case.
Curfews have been in place in some areas since June, and been extended to others due to the recent violence.
Tensions still simmer in part because the government has failed to find any long-term solution to the crisis other than segregating the two communities in some areas.
The United Nations called for calm Thursday in response to the new violence.
"The U.N. is gravely concerned about reports of a resurgence of inter-communal conflict in several areas in Rakhine State which has resulted in deaths and has forced thousands of people, including women and children, to flee their homes," U.N. Resident and Humanitarian Coordinator in Myanmar Ashok Nigam said in a statement.
Nigam said the United Nations was appealing for "immediate and unconditional access to all communities in accordance with humanitarian principles."
The statement said large numbers of people fleeing the new violence were headed for already overcrowded refugee camps currently housing about 75,000 people previously made homeless.
"Short term humanitarian support and action towards long term solutions are urgently required to address the root causes of the conflict," said the statement.
In Washington, State Department spokeswoman Victoria Nuland said the U.S. was deeply concerned about the reports of increasing ethnic and sectarian violence in Rakhine state and urged restraint.
The unrest broke out days after the U.S. held what it described as an encouraging human rights dialogue with Myanmar the latest sign of diplomatic re-engagement with the former pariah state, which has also seen the easing of sanctions to reward it for democratic reforms.
The unrest is some of the worst reported in the region since June, after clashes were set off by the alleged rape and murder of a Buddhist woman by three Muslim men in late May.
The crisis in Myanmar's west goes back decades and is rooted in a dispute over where the region's Muslim inhabitants are from. Although many Rohingya have lived in Myanmar for generations, they are widely denigrated as foreigners intruders who came from neighboring Bangladesh to steal scarce land.
The U.N. estimates their number at 800,000. But the government does not count them as one of the country's 135 ethnic groups, and so like neighboring Bangladesh denies them citizenship. Human rights groups say racism also plays a role: Many Rohingya, who speak a distinct Bengali dialect and resemble Muslim Bangladeshis, have darker skin and are heavily discriminated against.
The conflict has proven to be a major challenge for the government of President Thein Sein, which has embarked on democratic reforms since a half century of military rule ended in 2011.
It also poses a dilemma for the opposition New Light of Myanmar party of Nobel peace laureate Aung San Suu Kyi, which has been reluctant to go against the tide of popular anti-Rohingya sentiment. Suu Kyi has been criticized by some Western human rights advocates for failing to speak out strongly against what they see as repression of the Rohingya.
Buddhist monks have been spearheading anti-Rohingya protests, and on Thursday staged their latest one in Yangon, the country's biggest and most important city. More than 100 staged a peaceful protest at the historic Sule Pagoda.