The US Coast Guard was searching for two military helicopters that reportedly crashed off the Hawaiian island of Oahu while carrying a total of 12 people, officials said Friday, reports AFP. The Coast Guard was alerted late Thursday to the reported collision between two Marine Corps choppers carrying six crew members each, said Coast Guard spokeswoman Sara Mooers from Honolulu. Coast Guard search aircraft have spotted a debris field about 2.5 miles (four kilometers) off the north shore of Oahu but have found none of the crew members, she said. The Marine Corps said there was an "ongoing search and rescue" operation for the two CH-53 helicopters. The aircraft had been on a training mission. The aircraft involved in the accident were attached to Marine Heavy Helicopter Squadron 463 of the service's 1st Marine Air Wing in Hawaii. The Coast Guard sent a helicopter and an HC-130 Hercules plane to take part in the search. A Navy helicopter and a chopper from the Honolulu fire department joined the search, as did a rescue boat, Mooers said. US Marines have been involved in several helicopter mishaps in recent months. In September, one Marine was killed and 11 others injured when their CH-53E made a hard landing while training at the Camp Lejeune military base in North Carolina.