Coast Guard crews were searching on Thursday for five American Army aviators who went missing after their helicopter crashed during a training exercise about two miles off the Hawaiian island of Oahu, the authorities said.

The helicopter, a UH-60 Black Hawk, was reported missing late on Tuesday by personnel at the Wheeler Army Airfield on Oahu, who said that they had lost contact with the aircraft, the Coast Guard said in a statement.

Since then, debris from the helicopter has been plucked from the waters off Kaena Point, a nature reserve on the westernmost tip of Oahu, by search teams using helicopters, airplanes and boats.

The Black Hawk aircrew’s two pilots and three crew members were taking part in a night exercise with another Black Hawk crew between Kaena Point and Dillingham Airfield, a facility used by the military and the public and operated by the Hawaii Department of Transportation.