A fire that raced through a southern New Jersey neighborhood, killing two young sisters and burning six homes, apparently started in a duplex where the girls’ family lived, authorities said Friday.

The cause of the fire in Millville remains under investigation but does not appear to be suspicious, city Fire Chief John Wettstein said.

The children’s father was injured in the blaze, which took several hours to bring under control after first being reported around 11 p.m. Wednesday. Two houses had already been engulfed in flames when firefighters arrived, and the blaze soon spread to a third. The heat was so intense that it melted part of a fire truck and a parked car.

Firefighters’ initial efforts were hampered because a nearby hydrant wasn’t working, Wettstein said. Crews had to run about 800 feet (about 240 meters) of hose to another hydrant and nearly that length to a third to combat the blaze, which burned for several hours before it was brought under control.

The bodies of the girls, ages 8 and 10, were found Thursday afternoon amid the rubble, city officials said. Their names have not been released. Their father was being treated at a hospital for non-life-threatening injuries. His name also hasn’t been released

About two dozen residents were displaced by the fire. One woman said she and her three young children safely escaped their burning home because the blaze awoke her boyfriend, who was able to get them to safety.

Millville is around 30 miles (50 kilometers) west of Atlantic City.