LOS ANGELES, Jan. 26 (Xinhua) -- A Navy helicopter crashed into the Pacific Ocean about 50 miles off the California coast on Friday, killing at least one person on board.

    The fate of three other crew members aboard was unclear, a Navy spokesman said, adding that a search for them was underway.

    "We remain optimistic that we'll find the remaining three and that they'll be in good shape," said Cmdr. Jack Hanzlik. He, however, refused to release the name and rank of those aboard.

    The MH-60S helicopter, commonly known as a Seahawk, was on a training mission off the USS Bonhomme Richard near San Clemente Island, when it crashed at 2:45 p.m., according to Hanzlik.

    Referring to what type of maneuver the helicopter was performing when it crashed, he said, "They didn't crash into another aircraft or anything like that."

    The USS Bonhomme Richard is an amphibious assault craft that took Marines to Indonesia after the 2004 tsunami. The ship was training with two other Navy ships, destroyer USS Chung-Hoon and cruiser USS Chosin, according to Hanzlik.