MOSCOW, Feb. 23 (Xinhuanet) -- Nearly 50 people are now known to have died in the Moscow market roof collapse, it emerged, as rescuers using sniffer dogs and metal cutters continued to comb the wreckage.

    Emergency officials said it was unclear how many people were inthe building when the roof caved in at around 5:45 a.m. (0245 GMT).

    The Emergency Situations Ministry quoted by the Interfax news agency, said on Thursday afternoon that at least 48 people had been killed in the collapse and 31 others, including two rescue workers, had been injured.

    President Vladimir Putin has requested a thorough investigationinto the disaster and said rescuers were doing everything they could to help the victims, the Itar-Tass news agency reported.

    Police have sealed off the streets leading to the market, whichhas been all but demolished. Ambulances, bulldozers and cranes were standing by as rescuers with sniffer dogs cut through concrete blocks and metal beams to extract survivors. Some of those in the ruins were using mobile phones to help rescuers locate them. Rescuers also cut power transmission lines over the market to allow cranes to operate.

    Rescuers and machinery stopped working for a minute every half hour to listen for voices 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.

    Families of those doing business in the market waited anxiouslyfor news on the fate of their loved ones, many of them sobbing.

    A woman in her fifties told Xinhua she had been desperately trying to make contact with her younger sister who had been insidethe building when the roof went down. Another woman collapsed fromsorrow and anxiety but recovered a little with the help of relatives. Nearby, a father and son hugged each other tight in anguish.

    Emergency Situations Minister Sergei Shoigu, who came to the scene to oversee rescue work, said contact had been made with 10 people still alive under the debris. "They knocked, called back, and rescuers are now coming to them," he said.

    Viktor Beltsov, spokesman of the Emergency Situations Ministry,said heavy machinery would be used to remove much of the debris inseveral hours time.

    The city's emergency medical center has established a helpline to provide information on the dead and injured.

    Luzhkov earlier told reporters at the scene there was no evidence that the collapse had been an act of terror. Officials said heavy snowfall overnight, as well as design flaws, might be to blame for the collapse.

    The market was built some 30 years ago. The roof covers an areaof 2,000-3,000 square meters in the eastern Moscow district of Baumanskaya.

    A market worker, identified only as Bahrum, told Xinhua that onaverage about 500 people do business in the market during the day.If the roof collapsed later in the day, there would have been morecasualties, he said. Many of the market's business owners come from Central Asia and the Transcaucasia.

    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 and injuring more than 100. Enditem