San Diego ? A Navy helicopter doing training operations from a ship crashed 50 miles off the California coast Friday, killing one crew member and leaving three others missing long after darkness fell over the Pacific.

One sailor died after being pulled alive from the water, the Navy said.

A search-and-rescue operation was under way to locate the others, said Navy spokesman Cmdr. Jack Hanzlik.

The helicopter, based at Naval Air Station North Island, was on a training mission when it crashed at 2:45 p.m., Hanzlik said.

The MH-60S, commonly known as a Seahawk, was on a mission off the USS Bonhomme Richard near San Clemente Island.

Navy search-and-rescue efforts were under way as darkness fell. Rescue crews arrived at the crash site within minutes, Hanzlik said.