An old United Airline hangar at Newark Airport that was slated for demolition collapsed unexpectedly Wednesday afternoon, injuring four workers, Port Authority sources said.

The incident occurred at approximately 1:25 p.m., when the structure, commonly known as Building 332, or Hangar 14, came down without warning, officials said.

Nine people were working at the site and all were accounted for, but four were hurt and taken to University Hospital in Newark.

Two of those treated suffered injuries that were described as minor and none had injuries that were life-threatening, said Joe Pentangelo, a Port Authority spokesman.

The hangar, which has not been in use for at least 10 years, was scheduled to be taken down by Thursday, Pentangelo added.