MOSCOW — The snow-covered roof of a Moscow market collapsed early today, killing at least 40 people and forcing rescuers to clear away concrete slabs and metal beams to reach possible survivors trapped in the wreckage, officials said.

Rescue workers used metal cutters and pickaxes to break through the wreckage, calling through holes in search of survivors. Every few minutes, the rescuers turned off their electric generators and stood silently to listen for signs of life.

Medical workers inserted an intravenous drip to administer painkillers and other medications to a man trapped under a slab of concrete that left only his hand visible. Rescuers used heat guns to blow warm air into the rubble to try to prevent victims from succumbing to near freezing temperatures.

It was uncertain how many people were still trapped — dead or alive — under the wreckage. Emergency Situations Minister Sergei Shoigu said about 10 survivors were trapped earlier in the day, and they could be heard "knocking and crying out."

But officials have declined to say how many have been pulled out since then.

"There may be people alive under there but time is passing," Emergency Situations Ministry spokesman Viktor Beltsov said.