Rescuers reported spotting debris in the ocean off the island's westernmost Kaena Point
Five people are missing after a US Army helicopter reportedly crashed into the sea close to Hawaii.
Officials lost contact with the UH-60 Black Hawk helicopter at around 10pm, during a night-time training exercise off the coast of Oahu island.
The search began immediately, and rescuers later spotted debris in the ocean two miles from the island's westernmost Kaena Point.
A plane, two helicopters and several boats are now being used in the search. No unusual weather conditions were reported.
Night-time training of this kind is commonplace for helicopter crews, according to Lieutenant Colonel Curtis Kellogg, public affairs officer for the Army's 25th Infantry Division.
The loss of the helicopter was reported from the Wheeler Army Airfield near Honolulu, Hawaii's largest city, also on Oahu.
Another helicopter, also a part of the Army's 25th Combat Aviation Brigade, was also taking part in the exercise.
The UH-60 Black Hawk is a four-bladed twin engine utility helicopter, manufactured for the Army since the 1970s, by Silorsky Aircraft.