FORT WORTH, Texas (AP) — An explosion at a Texas hotel in Fort Worth on Monday littered downtown streets with large section of building and debris and injured 11, including one person who is in critical condition, authorities said.

Investigators believe the blast was caused by natural gas, said Bureau of Alcohol, Tobacco, Firearms and Explosives spokesperson Sara Abel, who was briefed by local police. Two people were in serious condition and the rest had minor injuries, authorities 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.

“There is a smell of gas in the area and there are windows and things that were blown outside of the structure,” said Craig Trojacek, a spokesman for the Fort Worth Fire Department.

Medics also treated four more people on the scene but did not take them to a hospital, said Desiree Partain of MedStar, which provides ambulance and emergency medical services in Fort Worth.

According to the hotel website, the Sandman Signature Fort Worth Downtown Hotel has 245 rooms and was built in 1920 as the “Waggoner Building,” named after cattle rancher and oilman William Thomas Waggoner. The building has been listed on the National Register of Historic Places since 1979.