At least 50 people were injured and up to four others are missing following an explosion Monday at a building in downtown Prague believed to have been caused by a gas leak, Czech emergency services officials said.

Four of the injured are in serious condition and the missing people may have been killed in the blast, emergency services director Zdenek Schwarz told the Pravo newspaper.

The explosion occurred just before 10:00 a.m. on Divadelni street next to the School of Film, District 1 Mayor Oldrich Lomecky said.

The building was being renovated and investigators believe the gas pipes were being inspected, Lomecky said.

The local official said he could not confirm whether a gas leak was to blame for the explosion.

The gas company shut off the supply of fuel to 20 buildings as a precaution.

Police officers and their search dogs have not been able to enter the structure due to concerns about the presence of gas.

The blast caused two floors in the building to collapse and affected the Academy of Sciences, which is on the other side of the street.

The explosion was felt several blocks away and more than 220 people were evacuated. EFE