LOS ANGELES -- Five US Marines aboard a helicopter that crashed in the mountains outside San Diego in the US state of California have been confirmed dead, according to updates of the US military.

The Marines were flying a CH-53E Super Stallion helicopter during a routine training flight from Creech Air Force Base to Marine Corps Air Station Miramar on Tuesday, when the aircraft was reported overdue, according to a release of the 3rd Marine Aircraft Wing.

The aircraft was located by civil authorities in Pine Valley, California, at 9:08 am on Wednesday.

Efforts to recover the remains of the Marines and equipment have begun and an investigation is underway.

"It is with a heavy heart and profound sadness that I share the loss of five outstanding Marines from 3d Marine Aircraft Wing and the 'Flying Tigers' while conducting a training flight last night," said Major General Michael J. Borgschulte, commanding general of the 3rd Marine Aircraft Wing, in a statement.

It was the second fatal crash for Marines in Southern California involving a Sikorsky CH-53E Super Stallion, a heavy lift helicopter, in the last six years, according to a Los Angeles Times report.