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."

Firefighters on the scene of explosion in Prague.
Firefighters on the scene of explosion in Prague. Reuters/David W Cerny
Injured workers in Prague
A police officer helps injured people near the area of a blast minutes after the explosion in Prague April 29, 2013. The explosion in central Prague on Monday injured about a dozen people and others were trapped in a building damaged by the blast, a Reuters witness and emergency services officials said. Reuters/David W Cerny
Injured woman after the explosion in Prague.
An injured woman after the explosion in Prague. Reuters/David W Cerny
An injured woman is pictured after the explosion in Prague
An injured woman is pictured after the explosion in Prague. Reuters/David W Cerny
An injured man removes his shirt in Prague
An injured man removes his shirt. Reuters/David W Cerny
Injured people near blast site in Prague
Injured people sit on a sidewalk near the area of the blast. Reuters/David W Cerny
Police at explosion site in Prague
Firefighters and police officers search an area. Reuters/David W Cerny
Injured people leave an area in Prague after explosion
Injured people leave the area. Reuters/ David W Cerny