A massive fire in a vacant three-story Brooklyn apartment house left a man dead and forced three neighboring families out of their homes, authorities said Wednesday.

The fire erupted around 8:40 p.m. Tuesday in the Cypress Hills neighborhood. The flames shot through the roof; area residents were warned to close their windows to avoid smoke exposure.

“When we arrived, there was heavy fire on the first, second and third floors,” FDNY Assistant Chief James Hodgens said. “We had to take a defensive position because of the structural instability of the building.”

Four people, three of them firefighters, were treated at hospitals for non-life-threatening injuries.

The Red Cross was providing aid to five adults and three children, including emergency housing for two of the three families, according to spokeswoman Desiree Ramos Reiner. They lived next door to the building where the fire started, she said.

The dead man, who had no identification, was found on the third floor of the building.

The city Buildings Department listed several complaints of squatters there, dating to 2002.

“Nothing was ever done. … Now my home is gone,” Tayleen Rosario, a pregnant mother of three who lived next door, told the Daily News.

The cause of the fire was under investigation.

(AP)