A house fire that left five Long Beach firefighters injured and caused extensive damage Wednesday morning was intentionally set, police and fire officials said.

Investigators were looking at the possibility that squatters inside the home on West Walnut Street in Long Beach had lit a fire to keep warm, he said. Police said firefighters who responded to the 6:12 a.m. 911 call found no one in the house.

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Detectives and fire marshals “determined the fire originated on the first floor and was intentionally set,” police said.

Nassau Assistant Chief Fire Marshal Michael Uttaro said two of the injured firefighters were taken to Long Beach Hospital. One had an ankle injury and was treated and released while the other, who complained of chest pain, was under observation.

He said police and fire officials ask anyone with information to call Crime Stoppers at 800-244-8377 or Long Beach police at 516-705-7370. All calls will remain confidential.

Nassau County fire officials said firefighters from Long Beach, Point Lookout-Lido, Island Park, Oceanside, Freeport, Baldwin, Rockville Centre, Lawrence-Cedarhurst, Inwood, Woodmere and East Rockaway helped battle the blaze.