NASHUA, N.H. – Three Nashua firefighters were injured in a natural gas explosion that led to a building fire at Greater Nashua Mental Health on Amherst Street Monday afternoon, according to state and city fire officials.

At about 2:15 p.m., members of the Nashua Fire Department responded to 440 Amherst St. for a report of a ruptured natural gas line. The caller said they could smell an odor of gas and heard a hissing sound.

Minutes after the initial crews arrived, an explosion injured three firefighters and caused the commercial building to catch fire. Forty people had to be evacuated from the building, according to a press release from the state Fire Marshal’s Office.

“At this time, investigators believe everyone who was inside the facility at the time of the blast has been accounted for and is safe. There is no ongoing threat to public safety in connection with this incident,” the release said.

While all aspects of the incident remain under investigation, investigators are looking into whether the gas line was damaged by falling ice, the release said.

As flames spread, mutual aid was requested from multiple surrounding communities. Due to safety concerns with the gas leak, the City of Nashua also issued an emergency alert to wireless phones and urged residents and visitors in the vicinity to refrain from using burners or other flames.

The firefighters who were hurt were transported to an area hospital with non-life-threatening injuries.

Multiple nearby roads were also closed while first responders secured the scene. Utility crews were ultimately able to shut off the damaged gas line, and the fire was under control by 6 p.m. The building was completely destroyed.

Anyone with information that may assist the investigation is encouraged to contact the New Hampshire State Fire Marshal’s Office at (603) 223-4289 or fmo@dos.nh.gov.