Two Marine helicopters collided off the Oahu coast in Hawaii late Thursday night, with 12 crew members on board. Marine Capt. Timothy Irish said that there were six passengers in each helicopter that were from the Marine Corps Base in Hawaii and that no other passengers were aboard the aircraft during the nighttime training mission.

Irish said that officials estimated a debris area spanning about two miles. The surf was choppy just before daybreak, according to the Miami Herald.

The Coast Guard is leading the search in coordination with some Navy and Air Force aircraft and a Honolulu Fire Department rescue boat.

Emergency teams had arrived at the scene just after midnight to find the remains of the wreckage burning in the water along with an empty life raft, according to The Washington Post.

Witnesses said they heard a loud boom over the water and saw a flash in the sky.

The search for the missing passengers is going to become an even more tedious task as a rough weather forecast indicates that waves as high as 30 to 40 feet are expected on Friday, according to CNN.

The helicopters involved in the collision were CH-53 helicopters, the Marine Corps' largest helicopter, which is capable of carrying more than 20 marines. The aircraft was assigned to the first Marine Aircraft Wing and has squadrons spread across the West Coast and the Pacific.