At least 57 people were found dead in the ruins of the roof over a Moscow market that collapsed on Thursday as rescuers using sniffer dogs and metal cutters continued to comb the wreckage overnight.

A policeman stands guard near the collapsed market in central Moscow Feb. 23. (Xinhua)

President Vladimir Putin has urged a thorough investigation into the collapse and said rescuers were doing everything they could to help victims, the Itar-Tass news agency reported.

Moscow Mayor Yuri Luzhkov said Thursday night work to clear the debris of the roof may take up to five days and a special technical commission had been set up to look into the disaster.

Luzhkov earlier ruled out a terrorist attack. "One thing is almost sure -- this is not an act of terror," he told reporters at the scene. Officials said heavy snowfall overnight, as well as design flaws, might be to blame for the collapse.

The snow-laden roof of the Bauman market, built some 30 years ago in eastern Moscow, caved in at around 5:45 a.m. (0245 GMT). Its roof covered an area of 2,000-3,000 square meters. Emergency officials said it was unclear how many people were in the market when it collapsed. Rescuers earlier spoke of dozens still trapped under the ruins.

The Emergency Situations Ministry, quoted by Itar-Tass, said late night Thursday that at least 57 people, including a child, were killed in the collapse and 33 others were injured.

Nine of the injured were released from hospital after treatment. Among the 24 still hospitalized, 13 remained in grave condition.

Ambulances, bulldozers and cranes were on call as rescuers with sniffer dogs cut through concrete blocks and metal beams to extract survivors. Powerful searchlight illuminated the site as darkness fell.

Rescuers and machinery stop working for a minute every half hour to listen to voice of survivors under the debris. Warm air was pumped into cavities of the collapsed building in a bid to keep those trapped alive amid freezing temperatures.

But as the city braced for another frigid night, rescuers said hopes of finding anyone alive were fading.

Outside police tape, families of those doing business in the market waited anxiously for word on the fate of their loved ones, many of them sobbing. The city's emergency medical center has established a helpline to provide information on the dead and injured.

Viktor Beltsov, spokesman of the Emergency Situations Ministry, said heavy machinery will be used to remove debris. Luzhkov said that work will "start at places where there are no people."

A market worker, identified only as Bahrum, told Xinhua that on average about 500 people do business in the market during the day. Many of the market's business owners come from Central Asia and the Transcaucasia. 

"If the roof collapsed later in the day when the market was opened to the public, there would have been more casualties," he said.

Itar-Tass said the market was designed by Nodar Kancheli, the same designer of the Transvaal water park whose roof collapsed in February 2004 killing 28 people.

Kancheli was quoted by Itar-Tass as saying on Moscow radio that the roof of the market had not been designed to bear a heavy load of snow.

"It seems there was a lot of snow, and nobody removed it," Kancheli said.

Editor: Yan