PRAGUE, July 17 (Xinhua) -- Two floors collapsed on Tuesday morning in a building under reconstruction in Mikulandska street in the city center of Prague, the capital of Czech Republic, with several people being buried.

Firefighters have freed three people, including one seriously injured, two in moderate conditions, but the numbers of those who may still stuck under the ruins are not known yet.

Prague police spokesman Jan Rybansky said another four worker might be under the debris, while rescuers spoke about another two. The cause of the accident will be investigated after the rescue operation.

The accident happened around 10:30 a.m. on Tuesday morning. All the three injured were rescued during the first hours of the rescuer's intervention and treated by an emergency service staff.