A strong explosion hit a building in Paris’ Left Bank, leaving at least 16 injured and igniting a fire that sent smoke soaring over city monuments and prompted the evacuation of surrounding buildings, police said.

The cause of the blast was not immediately known.

The facade of a building in the 5th arrondissement, or district, collapsed and emergency services were working to determine if anyone was still inside. The explosion hit near the historic Val de Grace military hospital.

Paris police chief told reporters there were 16 people injured, including 7 in “emergency condition”. The authorities did not specify whether the injured were in life-threatening condition.