A Marine helicopter crashed during a Southern California training mission and all four crew members were believed killed, the military said.

The CH-53E Super Stallion went down shortly after 2:30 p.m. Tuesday near El Centro, a few miles from the U.S.-Mexico border.

The helicopter was with the 3rd Marine Aircraft Wing out of the Miramar air station in San Diego, according to a base press statement.

The nearby Naval Air Facility El Centro messaged that the crash site was north of Plaster City, west of El Centro.

The cause of the crash is under investigation.