Rescuers on Friday searched for a missing crew member from a U.S. Coast Guard helicopter that crashed in ocean waters off Oahu, killing the three others on board.

The Coast Guard HH-65 Dolphin helicopter went down Thursday night while conducting search and rescue drills with a 47-foot motor lifeboat.

"This is a very difficult case because rescuers are being rescued," said Rear Adm. Manson Brown, 14th Coast Guard District commander.

There were no new developments from the overnight search for the missing crew member, said Coast Guard Petty Officer Luke Clayton.

The helicopter crashed about five miles south of Honolulu International Airport about 8:15 p.m. Thursday, according to the Coast Guard.

Witnesses aboard the lifeboat and a passing Air Force C-17 transport aircraft saw the crash.

Honolulu firefighters pulled the three crew members from the water and transported them to the Queen's Medical Center, where they were pronounced dead.

The victims were identified as co-pilot Lt. Cmdr. Andrew Wischmeier, rescue swimmer Petty Officer 1st Class David Skimin and flight mechanic Petty Officer 2nd Class Joshua Nichols, according to the Coast Guard. The name of the missing crewmember was not released.

"Coast Guard missions — even training missions — are inherently dangerous, and this aircrew was performing a drill in the weather conditions we are called into when we rescue others. It's a terrible loss," Brown said.

A Fire Department helicopter and two fire rescue boats joined the search at first light Friday, said Capt. Terry Seelig, spokesman for the Honolulu Fire Department.

The HH-65, manufactured by Aerospatiale, is 44 feet long and normally carries a pilot, co-pilot, flight mechanic and rescue swimmer. It is not capable of water landings.

The crash was the first Coast Guard helicopter accident in Hawaii since January 1982, when an HH-52 Sea Guard crashed into a cliff during a rescue mission in bad weather. Three people were killed.