A gas explosion ripped through a building containing offices and an art gallery in a historic district of central Prague on Monday morning, injuring 35 people and prompting evacuations of nearby buildings in the Czech capital, officials said.

More than 230 people were evacuated from the area, including from buildings used by schools including Charles University, officials said.

“We can now confirm this was a gas explosion. It was not a terrorist attack,” Prague Mayor Bohuslav Svoboda told reporters Monday.

The blast at 5 Divadelni Street, not far from the National Theatre and a block from the Vltava River, which cuts through the city, collapsed the first floor’s ceiling, officials said. Windows of neighboring buildings were damaged.

Officials do not believe anyone is trapped in the rubble, though fire officials will remain at the site for a while longer “to be 100% sure nobody is in there,” Svoboda said. People who initially were unaccounted for were later found with minor injuries, he said

Of the 35 people injured, 30 were taken to hospitals, including one man who suffered serious injuries, said Zdenek Schwarz, director of the city’s emergency services.

The city’s fire department, which is examining the area for possible gas leaks, said it would take two days to stabilize the site. Charles University canceled classes at an adjacent building for the rest of Monday.

Earlier, Czech news media gave conflicting reports of the building’s location, with an outlet reporting at one point that the blast happened at a film school building.

Marianna Zapotilova was in an office in a nearby building when the blast happened. The office’s window was open, and the force of the blast “pushed me away from my computer,” she said.

“There was a lot of dust” immediately after the explosion, Zapotilova said. “People in the area were injured, mainly by broken glass from the windows, they had their heads bandaged.”

— CNN’s Sarah Balter contributed to this report.