An Emergency Ministry spokesman put the death toll from the early morning accident at 56 with 32 injured. But emergency workers at the scene said the toll could rise further.

"People trapped are calling out. They are knocking. The trouble is: time is going by," Emergencies Minister Sergei Shoigu said at the scene, where rescue workers tried to locate survivors as another bitter winter's night loomed.

The building in Bauman district in eastern Moscow caved in at 5:45 a.m. (0245 GMT) after an overnight snowfall in the city which is undergoing one of its harshest winters in a generation.

President Vladimir Putin called for a "painstaking investigation" to find out down why the building collapsed.

The collapse came as vendors were setting out their stalls at the start of a national holiday. Many victims were market traders from Azerbaijan and other countries in the Caucasus.

"I woke up. There was some sort of big bang and everything was in darkness," said Halik Mamedov, 37, a herb seller who had been sleeping under a staircase in the market and managed to scramble to safety.

Mamedov estimated there were about 100 people in the market at the time while another worker who was allowed back in by emergency services told Reuters he saw bodies everywhere and put the death toll at about 55.

SNOW DESIGN

Moscow Mayor Yuri Luzhkov, who went to the scene, ruled out the possibility that the disaster was an attack by Chechen militants to coincide with the armed forces national holiday.

"We can safely say that the collapse of the market's roof is not a terrorist act," he said, adding it probably caved in because it could not bear the weight of the snow.

Luzhkov ordered checks at all buildings with similar roofs as it emerged that the architect who helped design the roof of the market, built in the 1970s, also designed the Transvaal Park swimming pool complex, whose roof collapsed in February 2004.

Nodar Kancheli was charged in April 2005 with negligence over the roof collapse at the Transvaal Park complex which killed 28 people and injured 200. He has denied responsibility.

Kancheli said the roof had not been designed to bear a heavy load of snow, but was questioned by prosecutors on Thursday.

"I was questioned as a witness and no charges were made," he was quoted as saying by the Itar-Tass news agency. "It seems there was a lot of snow, and nobody removed it," the agency quoted him as saying on the radio.

The main market building came crashing down onto an area of 2,000 square metres (21,530 sq ft), Russian news agencies said.

Anxious relatives awaited news outside police cordons and scanned survivor lists pinned to buildings.

Fifty rescue teams, including firefighters, were drafted in and lifting gear raised twisted girders and concrete blocks.

Survivors were said to be communicating from the debris by mobile phone to help rescue workers locate them.

"Everything just collapsed, I picked myself up and ran," said Rasim, whose brother was killed in the building.

Heavy snow has caused roof collapses elsewhere in Europe this winter, killing 66 people at an exhibition in Katowice, Poland, and 15 in an ice rink in Bad Reichenhall, Germany.