The Marine Corps says seven Marines were killed in a collision of two helicopters north of Yuma, Ariz., during night training.
Lt. Maureen Dooley with the Miramar Air Base in California says the Marines were based at Camp Pendleton north of San Diego.
She says the crash involved Cobra and Huey helicopters.
Authorities say it happened Wednesday evening.
Dooley says investigators were still gathering information early Thursday.
It will be at least 24 hours before the Marine Corps releases the names of those killed.