An old United Airlines hangar being demolished at Newark Liberty International Airport has partially collapsed, sending four workers to the hospital.

Port Authority of New York and New Jersey spokesman Joe Pentangelo says the collapse occurred early Wednesday afternoon.

He says the four workers had injuries that weren't considered to be life-threatening. Pentangelo says nine workers were inside the building at the time and all are accounted for.

No aircraft were in the hangar at the time.

Newark is a major hub for Chicago-based United.

The collapse is under investigation.