Two Marine helicopters with 12 on board were involved in a mid-air collision off the coast of Hawaii, U.S. military officials tell NBC News.
The two CH-53 Sea Stallion helicopters were conducting a nighttime training mission at the time of the accident. The crash happened off the coast of Haleiwa, located on the North Shore of Oahu.
Coast Guard rescuers spotted a burning debris field in the water and at least one empty life raft, but so far have found no sign of any survivors. Rescue efforts were hampered by darkness and high seas, officials said.
The cause of the crash has not been determined. According to the Weather Channel, there were light winds and scattered showers at the time of the collision.
The aircraft are from the 1st Marine Aircraft Wing from Marine Corps Base Hawaii.
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This story originally appeared on NBCNews.com