An explosion at a historic Texas hotel blew out windows, littered downtown streets with large sections of debris from the building and injured 21 people, including one who was in critical condition, authorities said.

The blast flung doors and entire sections of wall onto the road in front of the 20-story hotel, where rescue crews found several people trapped in the basement, said Craig Trojacek, a spokesman for the Fort Worth Fire Department.

More than 2 dozen rooms were occupied at the Sandman Signature Hotel when the blast took place, Trojacek said. Authorities said they believe a gas leak caused the explosion and said the hotel had been undergoing construction.

The blast left 4 people with serious injuries and the others taken to hospitals had minor wounds, officials said at a news conference.