At least 21 people were injured in the blast at the Sandman Signature Fort Worth Downtown Hotel, according to a spokesperson for MedStar as quoted by CNN, which provides emergency medical services and operates ambulances in the area.

The condition of one of the persons is critical.

"At approximately 3:32 p.m. multiple 911 calls were received for a fire at the Sandman Hotel located at 810 Houston St," Fort Worth Police posted on X page

"The Fort Worth Fire Department responded to the structure fire call and it was immediately updated to an explosion call at the same location. The Fort Worth Police Department assisted with street closures and clearing out parking garages in the immediate area," the police said.

"The latest report on injured individuals is 21. One of those was critical, four seriously injured and 14 of those were transported to a local hospital. One of the injured was self-transported to a hospital," the post said.

Police have started investigating the incident.

A woman at The Ashton Hotel in the region said the blast sounded like a huge firework.

“We heard the noise,” Cheila Sanchez told CNN. “It moved the hotel. I was like, ‘Whoa, what happened?’ Just heard this loud ‘boom!’ I didn’t know exactly what happened.”

At least two floors of the 20-storey building's facade were blown out onto the street and into a parking lot, local media reported.

Investigators believe the blast was caused by natural gas, Sara Abel, spokesperson with the Bureau of Alcohol, Tobacco, Firearms and Explosives, told local media as quoted by Xinhua.

"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, told the news agency.

The hotel opened last May following an extensive reconversion of the Waggoner Building which has been listed on the National Register of Historic Places since 1979, said the hotel's website, noting that "many of the original features" were retained during the reconversion.