HONOLULU — Two Marine helicopters collided off the Hawaiian island of Oahu with a total of 12 people on board and a search was underway Friday, military officials said.

Coast Guard Chief Petty Officer Sara Mooers said that the Marine Corps reported the crash just before midnight Thursday. Mooers says each aircraft had six people aboard.

A Coast Guard helicopter and C-130 airplane arrived on scene 2 1/2 miles offshore shortly after midnight and located a debris field.

Mooers said a Navy helicopter, a Honolulu Fire Department rescue boat have also responded and Coast Guard cutters are coming in.

Marine Capt. Timothy Irish confirmed that a search and rescue is underway for the two CH-53Es — transport helicopters. He said the aircraft were from the 1st Marine Aircraft Wing from Marine Corps Base Hawaii.

Mooers told Los Angeles radio station KNX-AM that search conditions were challenging because of darkness and high surf. She said a high surf advisory is in effect for waves 10 to 15 feet building throughout the morning.

There was no immediate word on what caused the collision or if any survivors have been found.

The collision comes less than a year after the Marine Corps’ new hybridized airplane-and-helicopter aircraft crashed during a training exercise, killing two Marines. The MV-22 Osprey went down last May with 21 Marines and a Navy corpsman on board.