Twelve dock workers and a firefighter sustained minor to mild injuries after a container ship leaked a hazardous material in the Port of Long Beach.

City Fire Department spokesman Brian Fisk said a 6,000-gallon container on the Harbour Bridge ship began leaking the liquid Sunday morning.

The Coast Guard identified the liquid as propyl acetate, primarily used as a solvent. It's unclear how much spilled or what caused the leak.

This photo courtesy of the Long Beach Fire Department shows firefighters boarding a ship responding to an hazmat incident in the Port of Long Beach, Calif., Sunday, Aug. 6, 2017. Long Beach firefighters treated 11 workers and one firefighter for exposure to some hazardous material fumes, at Pier G, where a flammable liquid leaked from a 6,000 gallon tank on a container vessel. Two persons have been taken to a hospital. (Brian Fisk/Long Beach Fire Department via AP)

Fisk says the leak was contained and a 1,000-foot perimeter was established as a precaution.

Eleven dock workers were treated for minor injuries at the scene while one was taken to a hospital with mild injuries. A firefighter was injured in a fall at the scene.

Local and federal officials are investigating the spill and monitoring cleanup efforts.