3 firefighters injured in explosion at Nashua, New Hampshire building

Three firefighters were injured in an explosion at a building in Nashua, New Hampshire on Monday afternoon. Firefighters initially responded for an odor of gas inside 440 Amherst Street.

"When they arrived on scene, they quickly called for more resources. A Mayday was transmitted once the explosion took place," Nashua Fire Chief Steve Buxton said.

The firefighters were taken to the hospital with what are believed to be non life-threatening injuries.  

Buxton said there were approximately 40 people inside the building at the time, and they have made contact with all but four of them. 

Footage from WBZ-TV's helicopter showed flames and heavy smoke billowing from a building.

"Shelter in place if in the vicinity," the city of Nashua's Office of Emergency Management said in a social media post.

The fire department in nearby Merrimack said there was a "natural gas explosion" in the building and urged residents to avoid the area.