GARDNER, Mass. (WHDH) -- Firefighters battled a four-alarm fire in Gardner that left seven people homeless and a building in ruins on Monday.

Fire broke out at a triple-decker building on Pleasant Street around 3 a.m. Monday. The fire started in the basement of one building and quickly spread to the second building.

“I heard two bangs. That was it. The roof caved in,” said Cathy Marcharda. “It was black smoke everywhere. I had to stand over there. It was pretty intense.”

Frank Lechtonen was awakened from a deep sleep by a horn beeping and someone yelling fire.

“Then a policeman or someone came to my door and said ‘You have to get out.’ I said, ‘I wanna grab something.’ He said, ‘No,’” said Lechtonen.

The city tore down one of the buildings because of its instability.

Investigators continue to investigate the basement apartment, where they say the fire started. The intensity of the fire leads investigators to believe that something is off.

“We knew the apartment was empty and there’s question that even the electricity was shut off so we’d still like to get in there and see,” said fire chief Ron Therrien.

Because of hotspots, fire officials believe that won’t happen until Tuesday.

“I’m thinking glad I just moved out of the third floor and that a friend just moved out of the second floor where she would have had five children and I have had one,” said Mandy Gallant, a former tenant.

The fire chief said there are no known code violations in the building.

No one was injured in the blaze. The Red Cross is assisting the families.