Emergency crews are continuing to respond to a dangerous and developing situation in Nashua, New Hampshire, after a gas leak sparked a fire and explosion at a commercial building on Amherst Street.

The incident occurred at 440 Amherst Street, a busy area on the city’s west side. Officials say the explosion was caused by an apparent gas leak inside the building, which houses the Greater Nashua Mental Health Center. Flames and heavy smoke were visible as firefighters worked to control the blaze.

During the response, three firefighters were injured. Authorities confirmed that one firefighter sustained serious injuries, while two others were treated for injuries not considered life-threatening. All were transported to area hospitals.

Because the gas leak is still being addressed, officials issued an emergency alert, warning residents and businesses nearby to avoid open flames, shut off burners, and be prepared to evacuate if conditions change. Police have also urged drivers to avoid the Amherst Street area and seek alternate routes as emergency crews remain on scene.

Nearby buildings, including a charter school in the area, were placed under shelter-in-place orders, and officials later confirmed that everyone inside those facilities was accounted for and safe.

Fire departments from Nashua and surrounding communities are assisting in the response. The building has suffered significant damage, and authorities say the situation remains active and under investigation as crews work to fully secure the area and eliminate any remaining hazards.

Residents are being asked to continue following instructions from local officials as this ongoing emergency unfolds. Updates will be provided as more information becomes available.