 An explosion at a historic Texas hotel in Fort Worth on Monday 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-storey hotel, where rescue crews found several people trapped in the basement, said Craig Trojasek, a spokesman for the Fort Worth Fire Department, more than two dozen rooms were occupied at the Sandman Signature Hotel when the blast took place, Trojasek said. Authorities said they believe a gas leak caused the explosion and said the hotel had been undergoing construction. The blast left four people with serious injuries and the others taken to hospitals had minor wounds, officials said at a news conference. The Sandman Signature Hotel is in a busy area of downtown about one block from the Fort Worth Convention Center. Footage from news helicopters showed firefighters picking their way through the piles of drywall, shattered glass and mangled metal that coated the street outside the hotel. Authorities urged people to avoid the area.