The U.S. Marine Corps says seven Marines were killed when two helicopters collided during night training near the border of California and Arizona.

Authorities say it happened Wednesday evening.

Lt. Maureen Dooley with the Miramar Air Base in California says the crash involved Cobra and Huey helicopters.

It will be at least 24 hours before the Marine Corps releases the names of those killed.

Dooley told CNN that helicopter teams train in the area because it mimics conditions in Afghanistan.

When asked whether the crash was a result of technical or pilot error, she said she couldn't confirm anything because the investigation had just begun and could take months.

Capt. Staci Reidinger, director of public affairs at Marine Corps Air Station Yuma, said the crash was not in a populated area.