The crash is said to have occurred during a routine training mission
Four US marines are believed to have been killed in a helicopter crash in southern California.
The Marine Corps CH-53E Super Stallion helicopter from the 3rd Marine Aircraft Wing (3rd MAW) crashed near El Centro at 2.35pm local time (10.35pm Irish time) on Tuesday.
In a statement, the Marine Corps said all four of the crew were presumed dead.
An investigation is under way into the cause of the crash.
In a statement, the 3rd Marine Aircraft Wing said it will wait 24 hours after families are informed before the victims' names are released to the media.
A post on El Centro Naval Air Facility's Facebook page said: "Our thoughts and prayers go out to the families and friends affected by the tragedy earlier today."
The manufacturer Lockheed Martin says the helicopter is primarily designed to lift heavy objects, such as military vehicles, from ship to shore.
The 3rd MAW said the crash occurred during a routine training mission.
The Desert Review reported it came down about 10km from Plaster City in Imperial County, about 20km west of the air base and about the same distance north of the Mexican border.