Amateur footage posted online by activists showed flames raging through the stone passageways, the wooden doors of shops crackling in the heat as rebels struggled to put out the blaze with a garden hose. Other videos showed a pall of smoke hanging over the city's skyline.
The fire started late Friday amid heavy government shelling, and was still burning Saturday morning, activists said. One, who is based in the city, estimated that the majority of the neighborhood's hundreds of shops were destroyed.
"It's a disaster," said Ahmad al-Halabi, speaking from the site by telephone. "The fire is threatening to spread to remaining shops." Syrian authorities had cut the city's water supply, he added, making it more difficult to put out the flames. He said rebels and civilians were working together to control the blaze with a limited number of fire extinguishers.
"It is a very difficult and tragic situation there," he said. "There are narrow, hard to reach streets where the fire is still burning."
The market, stretching over several kilometers around the towering 13th century citadel, once bustled with shoppers and tourists. But after shelling and fighting in the area intensified a month ago, most stands closed. On Saturday, shop owners were scrambling to rescue whatever stocks they had left there in storage.
Once considered a bastion of support for Syrian President Bashar Assad's regime, Aleppo has in the last two months become the focus of the insurgency. Its fall would give the opposition a major strategic victory, with a stronghold in the north near the Turkish border.
Since the rebel offensive began in August, each side has controlled about half of the city and has repeatedly tried but failed to capture the rest.
Rebels launched Thursday what they said would be a "decisive battle" to drive Assad's forces out of Aleppo and fighting has since spread to wide swaths of the city.
The Aleppo souks are not the only Syrian cultural treasures to have fallen victim to the chaos of the country's uprising and the crackdown by the Assad regime.
Some of the country's most significant sites, including centuries-old fortresses, have been caught in the crossfire between regime forces and rebels. Others have been turned into military bases, raising archaeologists' fears of damage.
Regime shelling of neighborhoods where the opposition is holed up has smashed historic mosques, churches and souks in central Homs province and elsewhere the country. Looters have stolen artifacts from excavations and museums.
Rodrigo Martin, an expert in ancient Syrian historical sites, said all six of Syria's UNESCO world heritage sites have suffered varying degrees of damage since the start of the uprising.
Rami Abdul-Rahman, who heads the Syrian Observatory opposition group, said it was not clear how the fire at the Aleppo market was started, that at least 200 shops had burned. The group relies on a wide network of activists on the ground.
The claims could not be independently verified because of limitations on the work of journalists in Syria.
Fighting continued in many parts of Aleppo Saturday and activists said at least three people were killed, including two rebel fighters. Syria's state-run news agency SANA said soldiers were pursuing military operations against armed groups in Aleppo and its outskirts, inflicting heavy losses on the "terrorists," the term used by authorities to refer to rebels.
In the Damascus suburb of Qudsaya, activists said the bodies of at least eight men were found who appeared to have been summarily executed, but the circumstances were not immediately clear.
The Syrian uprising began in March 2011 with largely peaceful protests but has since transformed into an insurgency and civil war that has defied all attempts at a diplomatic solution. Activists say more than 30,000 people have been killed.
Al-Halabi, the Aleppo activist, said overall fighting in Aleppo had eased on Saturday compared to the previous two days, although shelling and clashes continued in several locations.
"Both sides seem to be trying to catch their breath after the intensity of the past two days," he said.