Three or four people may have been killed and some 40 injured after a powerful explosion tore through a building in the center of the Czech capital Prague on Monday, April 29, head of the rescue service in Prague Zdenek Schwarz said, according to RIA Novosti.

The explosion took place around 10 am local time in a building on Divadelní Street in Prague’s Old Town, close to the river. The cause of the explosion is not yet clear but some reports said there was a gas leak in the building, Radio Prague said earlier.

Response teams including fire fighters, ambulances and police arrived at the scene within minutes of the explosion, the city’s emergency services said.

The police have cordoned off the area.

The blast shattered windows in nearby buildings and forced the evacuation of the area.