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-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 two 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. Rebecca Martinez was among those in nearby buildings who recalled hearing a loud crack that sounded like thunder Monday afternoon, and then seeing a wall of dust and debris sweep through the city streets. Stepping outside to see what happened, she came upon a man and a woman leaned up against a fire hydrant.