PHOTOS: An explosion that blew out at least two floors of a high-rise hotel and injured nearly two dozen people in downtown Fort Worth on Monday afternoon is suspected of being caused by a natural gas leak, according to the ATF and Fort Worth Fire Department. The explosion was reported at the Sandman Signature Fort Worth Hotel in the 800 block of Houston Street at about 3:30 p.m. Officials confirmed Monday afternoon that 21 people were injured in the blast, including one critically and four seriously. Glass and exterior walls from at least two floors of the building's 8th Street facade were blown out onto the street and into a parking lot on the west side. The explosion appears to have also damaged the sidewalk, exposing the building's lower floors.