Although the market had not yet opened to the public, survivors say some 150 traders were inside. The market was preparing for a particularly busy day today, which is a popular national holiday in Russia, Defenders of the Fatherland Day.
Vendors were also working in some parts of the market that are used overnight for wholesale trading.
"We can say with complete certainty that this was not a terrorist act," Moscow Mayor Yury Luzhkov said at the site today. "According to survivors, there was a cracking sound and then the roof began to collapse. So, most likely it was caused by roof overload or old constructions."
Investigators are studying three possible causes of the collapse: failure to clear heavy snowfall from the roof, improper maintenance of the building, and construction mistakes.
Russian media reported that an additional platform for housing more market stalls had been built and attached to the roof in violation of building regulations.
The Baumansky market was designed in the 1970s by Nodar Kancheli, the same architect who drafted the plans for a Moscow aquapark where the roof collapsed two years ago, killing 28 people. Prosecutors have blamed that collapse on design flaws.
"I can't say whose fault it is -- maybe it is snow, or maybe it is maintenance," Kancheli said today. "I can't imagine how it was standing for 30 years and now [it collapsed]. The roof was designed to carry a snow load of 140 kilograms. Now, [roofs] are designed to hold 220 [kilograms of snow]. Standards have changed or maybe there's more snow now."
Rescue efforts were hampered later in the day when a fire broke out inside the building, possibly caused by sparks flying from the metal cutters used by rescuers to clear the rubble.
Police sought to reassure anxious people searching for relatives or colleagues feared to be still trapped under the wreckage. Several times, police officers had to prevent them from penetrating cordons enclosing the site.
Luzhkov said most of the victims appeared to be immigrants.
The vast majority of traders working at Moscow markets come from the former Soviet republics in Central Asia and in the Caucasus, particularly Azerbaijan.
A Russian woman who regularly shopped at the Baumansky market told RFE/RL's Uzbek Service that the market was mainly run by Uzbeks and Azerbaijanis, who often spent whole nights in the building.
"Among us Russians, it is considered an Uzbek market," the woman said. "It is [also] a wholesale market. At night, they tied [bunches of] onion, parsley, dill, they spent the night there, they slept and grew [greens] in the basement, that's why there were people inside. They guarded [the building]. They were mainly Uzbeks and Azerbaijanis, there were no Russians."
According to the head of Moscow's Azerbaijani diaspora, 31 Azerbaijanis have been confirmed dead and 27 injured. Others could still be trapped under the rubble.
A Georgian television channel earlier today reported that at least nine Georgian nationals are likely to have been in the market when the roof collapsed.
(RFE/RL's Uzbek Service correspondent in Moscow, Gulasal Kamalova, contributed to this report)
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