Two US Marine helicopters have collided near the Hawaiian island of Oahu, each with six people on board. <br /> <br />The crash occurred during a night-time training mission late on Thursday but it is unclear why. <br /> <br />Coast Guard Chief Petty Officer Sara Mooers said debris was seen in the ocean. <br /> <br />Marine Capt Timothy Irish told the Associated Press news agency that a search and rescue was under way for the two CH-53 transport helicopters. <br /> <br />The aircraft were from the 1st Marine Aircraft Wing from Marine Corps Base Hawaii, he said. <br /> <br />Ms Mooers told Los Angeles radio station KNX-AM the search would be tough because of darkness and a high surf advisory. <br /> <br />Less than a year ago, a Marine Corps MV-22 Osprey crashed during a training exercise, killing two Marines.
