There was a large explosion in an office building in central Prague on Monday at about 10 a.m. local time, on Divadelni Street, near the east bank of the Vltava River, the Associated Press reported.

As many as 40 people have been injured, and police believe there are still others trapped in the rubble. No deaths have been reported yet. Police spokesman Tomas Hulan told AP the blast was likely caused by a natural gas explosion. The building subsequently collapsed.

At least four people had serious injuries, the head of the rescue team told AP. Firefighters were also reportedly using sniffer dogs to find any survivors. "There is an unknown number of injured and trapped people," Jirina Fikejzova, Prague emergency services spokeswoman, told Al-Jazeera.

The blast blew out windows in the surrounding buildings and covered the street in rubble. 

Czech Prime Minister Petr Necas said in a statement he was "deeply hit by the tragedy of the gas explosion."