Originally Published: 09 JAN 24 11:10 ET

By S.E. Jenkins, Jason Allen

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FORT WORTH, Texas (KTVT) -- Twenty-one people were injured Monday as a result of a gas explosion at a historic downtown Fort Worth hotel, according to police.

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.

"At first I thought it was thunder. I heard this loud noise and then I looked out of my room and I saw it wasn't thunder," said Christa Daniels, who witnessed the explosion. "And then I saw the people running. And then after that, I saw all of this debris just flying all around the place.

Twenty-one people were injured as a result of the explosion, J. Pollozani with the Fort Worth Police Department said Monday night. One patient is reported as critically injured and four are seriously injured. All the other patients reported minor injuries.

According to FWFD, 19 patients were treated on the scene, one took themselves to a hospital and there are not any deceased officials are aware of at this time.

"I saw several individuals covered with blood and they were placed in the ambulance," Daniels said. "Then you had others that were just crying uncontrollably ... It took me back to 911. And that was a frightening thing."

Three of those injured were employees of Musume, the restaurant inside the Sandman Hotel.

"All of us at Musume are devastated by the tragic explosion that took place this afternoon at the Sandman Signature Hotel, which is the home of our restaurant," said Josh Babb, co-founder of Musume. "Luckily, Musume was closed during the time of the explosion, so we had no customers dining and limited employees working. Three Musume employees were injured, but are being treated in the hospital and in stable condition."

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.

"I thought it was a bomb," Daniels said. "Honestly, I really thought it was a bomb. And then I started smelling the gas. The gas was very, very strong."

Fort Worth Police said a family reunification area is at Sundance Square, located at 420 Main St.

"If you have a loved one you cannot get in touch with, go to Lot 15 at the Sundance Square parking lot," Trojacek said.

The hotel was operational at the time of the explosion and there were 26 rooms occupied.

Trojacek said they found an individual the hotel manager reported as unaccounted for, and another person officials did not know was unaccounted for was also found.

"Several people were extracted from the basement that weren't able to get out on their own," said Trojacek.

CBS News Texas' 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.

The explosion was powerful enough that it blew concrete off the street level, allowing firefighters to peer down into the levels below ground.

"There was a live fire in the building that has been extinguished," said Trojacek. "It did go to a second alarm and that allowed us to bring in more resources to help with patient care... to make sure we were doing a search of the entire building and to put the fire out."

Governor Greg Abbott released the following statement:

"The State of Texas is in close contact with Mayor Parker, Sheriff Waybourn, and other local partners and first responders in Fort Worth to assist with emergency response efforts following the tragic explosion at the Sandman Hotel. We continue to monitor the situation and stand ready to immediately deploy any additional personnel and resources needed to keep Texans in the area safe and out of harm's way. Cecilia and I ask all Texans to pray for those who were injured in the explosion, as well as those bravely responding to keep others safe."

"This is still a very active scene ... We have been working in collaboration with ATF, the FBI, with our Arson and Bomb Division as well. We have not made a 100% determination but wanted to make clear that this was some type of gas explosion and we are still working on the details of that to figure out what all caused that at this point in time," Trojacek said.

The gas odor was evident downtown for hours after the blast.

Atmos Energy said highly trained technicians also responded and that "gas has been isolated to the affected area, and it will continue to assist the Fort Worth Fire and Police Departments and all officials in support of their investigation."

"I am deeply proud of the swift and professional response from our [Fort Worth] and area first responders today," wrote Mattie Parker, the mayor of Fort Worth. "I am humbled by the offers from our state leadership to support our city."

Northland Properties, the company that owns the Sandman Hotel, released the following statement to CBS News Texas:

"We are working closely with the authorities to understand the origin of the event and the extent of the harm caused. The safety and well-being of our team members and guests is our priority. We are working with those who have been injured to fully support them at this time."

FWFD said search efforts will continue throughout the night to ensure no one is trapped. The fire department and other agencies will remain on scene all night and there are no public safety concerns for anyone in the downtown area regarding the explosion.

The investigation is ongoing.

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