The concave, snow-covered roof of a Moscow market collapsed early Thursday, killing at least 27 people and trapping about 10, officials said. Rescue workers used metal cutters and hydraulic lifters to clear the ruins of steel and concrete pieces. Workers used pickaxes to cut holes in the wreckage and knelt to call into the holes in search of survivors. Mayor Yuri Luzhkov, who went to the site to oversee rescue efforts, said terrorism was unlikely. "Chances are more than 90 percent that a terrorist act can be ruled out," he told reporters. "It was a technical accident." Twenty-five people were injured and most of them were hospitalized, emergency officials said. 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. Trapped survivors were using mobile phones to call their relatives, helping rescuers zero in on their location, said Yuri Akimov, deputy head of the Moscow department of the Emergency Situations Ministry. The victims were municipal and market workers, and Mayor Yuri Luzhkov said all the dead were guest workers from outside Moscow. Channel One said they had spent the night in the market, which was not open for retail business. Ekho Moskvy radio reported that there could also have been wholesale buyers in the building. Some of those under the rubble were alive, Emergency Situations Minister Sergei Shoigu told reporters at the scene. "They're knocking and crying out," he said. Investigators were looking at three possible causes of the collapse: improper maintenance of the building, a build up of snow and errors in the building's design, Moscow prosecutor Anatoly Zuyev said. Five to 8 centimeters (2-3 inches) of wet snow had fallen overnight, on top of 47 centimeters (18.5 inches) that had fallen since the start of winter, the Russian Weather Service said.