MOSCOW - The roof of a Moscow market collapsed early Thursday, killing at least 12 people and trapping an unknown number of people under the wreckage, emergency officials said.

It was unclear how many people were in the Bauman market in eastern Moscow when the roof collapsed at 5:20 a.m., the duty officer at Russia's Emergency Situations Ministry said. The official, speaking on customary condition of anonymity, said the toll could have been worse had the market been open for business.

Ministry spokesman Viktor Beltsov told The Associated Press that at least 12 people were killed and 17 injured.

Moscow city prosecutor Anatoly Zuyev said up to 40 people could still be trapped in the wreckage, the RIA-Novosti news agency reported.

Investigators believe heavy snow on the roof caused it to collapse, officials said. A wet snow had fallen in Moscow for much of the day Wednesday and overnight.

The head of the Emergency Situations Ministry, Yuri Akimov, told state-controlled Channel One television that survivors were using mobile phones to help rescuers find them. Rescuers were also using sniffer dogs.

"It's still not possible to use heavy equipment to sort through the wreckage, since there are living people there," Akimov told Channel One.

Russian media said the entire roof, covering an area of about 2,400 square yards, had fallen onto the market stalls. Most of the victims were believed to be municipal and market workers, though Ekho Moskvy radio said there could also have been wholesale buyers in the building, as well.

The collapse occurred on Defenders of the Fatherland Day, a Russian state holiday honoring the armed forces.

The Interfax news agency said the market had been designed in the 1970s by Nodar Kancheli, the same architect who drafted the plans for Moscow's Transvaal water park, where the roof collapsed in February 2004, killing 28 people. Prosecutors have blamed that collapse on design flaws. -AP