At least 11 people were injured Monday following a possible gas explosion at a downtown Fort Worth hotel, according to the fire department.

The first call came in at 3:32 p.m., followed by multiple calls reporting a “type of explosion” at the Sandman Hotel, located at 810 Houston St., according to the Fort Worth Fire Department.

There are as many as 11 patients, according to MedStar. One patient is reported as critically injured and two are seriously injured. All of the patients have minor injuries. Nine patients have been transported to local hospitals.

Although the area smelled like gas following the explosion, the initial cause is still under investigation, said Craig Trojacek, the public information officer for the FWFD.

“There is a smell of gas here in downtown. We’re not sure if the smell of gas was caused from the explosion or the fire itself, or if that’s what caused the explosion,” Trojacek said. Fort Worth Police said a family reunification area is being established at Sundance Square, located at 420 Main St.

All Tarrant County offices in downtown are now closed. Jason Allen spoke to a man who was in the hotel at the time of the explosion. He did not want to go on camera, but said there was a smell of natural gas before the explosion and he remembered asking one of his teammates, ‘Do you smell natural gas?’

He said the scent wasn’t strong, but they smelled it. He said the smell came from beneath them. Then, the whole second floor filled with dust and smoke. They could see the red EXIT sign and found the stairwell.

He told CBS News Texas that when he and the people he was with got to the stairwell, most of it was missing so they jumped five or six feet down and were able to make their way out of the building.