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Audrey McAvoy, Associated Press
Military officials and Honolulu Police Department officers talk at a beach park where search and rescue officials are meeting in Haleiwa, Hawaii, Friday, Jan. 15, 2016, after two U.S. Marine helicopters carrying 12 crew members collided off the Hawaiian island of Oahu during a nighttime training mission. Rescuers were searching a debris field in choppy waters Friday, military officials said.

HALEIWA, Hawaii — Two Marine Corps helicopters carrying six crew members each collided and went down off the Hawaiian island of Oahu while on a nighttime training mission, and rescuers searched choppy waters Friday where debris had been sighted, military officials said.

There was no immediate word on the fate of those aboard or what caused the accident.

The transport helicopters known as CH-53Es crashed just before midnight Thursday, officials said.

A Coast Guard helicopter and C-130 airplane spotted a debris field 2 1/2 miles offshore early Friday. The debris covered an area of 2 miles, Marine Capt. Timothy Irish said.

The choppers are part of the 1st Marine Aircraft Wing. Known as Super Stallions, they are the U.S. military's largest helicopter, capable of carrying a light armored vehicle, 16 tons of cargo or a team of combat-equipped Marines, according to a Marine Corps website.

The search included aircraft from the Navy and Air Force, a Honolulu Fire Department rescue boat and Coast Guard cutters, officials said.

About two dozen Marines gathered Friday morning on the beach at Waimea Bay, a popular surfing spot a few miles from the rescue operation.

A steady rain was falling on the North Shore just before daybreak, and rough water conditions were forecast.

A swell approaching the area was to bring dangerous 30- to 40-foot waves to beaches and 10- to 20-foot seas near the rescue operation, National Weather Service meteorologist Matthew Foster said. Winds were expected to be relatively calm at 10 mph or less.

The crash comes less than a year after the Marine Corps' hybridized tilt-rotor aircraft crashed in during a training exercise, killing two Marines. The MV-22 Osprey went down last May with 21 Marines and a Navy corpsman on board.

In 2011, one serviceman was killed and three others were injured when a CH-53D Sea Stallion chopper crashed in Kaneohe Bay, Hawaii.

Associated Press writers Caleb Jones in Honolulu, Greg Keller at Waimea Bay, Bob Lentz in Philadelphia and Mark Thiessen in Anchorage, Alaska, contributed to this report.