NASHUA, N.H.- The State Fire Marshall’s office says three Nashua Fire fighters were injured Monday afternoon in a natural gas explosion and fire.

Around 2:15 Fire crews answered a call for a ruptured natural gas line at the Greater Nashua Mental Health building at 440 Amherst St. which led to workers evacuating the building after smelling gas and hearing a hissing sound.

The fire and explosion ended up destroying the building. Fire crews reportedly had the fire under control by around 6pm, but say that three fire fighters were injured, one seriously, all of which were then taken to the hospital, however one firefighter was released while the other two remained at the hospital overnight.

An emergency alert was sent to cellphones across southern New Hampshire a little after 2:30 Monday afternoon, warning of a potential gas leak. The alert urged people in the area to extinguish burners or other flames, avoid the area and prepare to evacuate.

Fire investigators are scheduled to be back on the scene Tuesday.