Rescuers are searching the sea for 12 crew members after two US Marines helicopters collided off the Hawaiian island of Oahu.

Coast Guard Chief Petty Officer Sara Mooers said the Marine Corps reported the crash and added that each aircraft had six people aboard.

A Coast Guard helicopter and C-130 plane has located debris in the water.

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

Marine Captain Timothy Irish confirmed that a search and rescue was under way for the two CH-53E transport helicopters, from the 1st Marine Aircraft Wing at Marine Corps Base Hawaii.

Ms Mooers said search conditions were challenging because of darkness and high surf. She said an advisory was in effect for waves up to 15ft.