First responders after a reported explosion in Fort Worth, Texas, on Monday|Cardboard0G|X

An explosion at Fort Worth’s Sandman Hotel left two dozen people injured on Monday afternoon. No fatalities were reported, but the Fort Worth Fire Department confirmed 21 injuries; one person was in critical condition and four others were seriously injured.

The cause remains unclear, though authorities suspect a gas explosion.

Around 26 out of 245 hotel rooms were occupied at the historic 104-year-old building when the explosion occurred.

The Sandman Hotel has been listed on the National Register of Historic Places since 1979.