WEST MILFORD, N.J. (AP) — Five people were transported to hospitals after an explosion at a New Jersey home on Friday night, police said.

The house in West Milford was heavily damaged by the explosion around 9 p.m., the West Milford Police Department said in a statement.

A sixth person at the scene refused additional medical treatment, police said.

West Milford Deputy Fire Chief Rich Poplaski said the structure collapsed as a result of an “unknown cause,” northjersey.com reported.

West Milford is located about 33 miles (53 kilometers) north of Morristown, New Jersey, and 48 miles (77 kilometers) northwest of New York City.

Police said the victims were transported by helicopter, including two to Morristown Medical Center, one to St. Joseph’s University Medical Center in Paterson, New Jersey, one to Cooperman Barnabas Medical Center in Livingston, New Jersey, and one to Hackensack University Medical Center in Hackensack, New Jersey.

The explosion is under investigation by West Milford detectives and the fire marshal’s offices from the town and state, police said.