The search continued Sunday for a 21-year-old airman who disappeared Saturday while swimming off Tarague Beach on Andersen Air Force Base, Guam.

Airman 1st Class Michael McDonald was last seen in distress around 11:15 a.m., according to a Guam Coast Guard news release. McDonald was with four companions at the time of the incident, three of whom made it to shore safely. The fourth airman was rescued, transported to Naval Hospital Guam, treated and released, according to Coast Guard spokesman, Lt. j.g. Marcus Hirschberg.

A high surf advisory issued by the National Weather Service for Guam has been in effect for more than a week and remained so until Tuesday.

The Coast Guard cutter Assateague, Navy helicopters from Helicopter Sea Combat Squadron 25, and a P-3 Orion surveillance aircraft from Kadena Air Base, Okinawa, were conducting the search. Guam fire and police department personnel also joined the search on land Saturday.

“We are still actively searching,” Hirschberg said early Sunday evening. “The cutter will remain on the scene until the airman is found or until the search is suspended.” He had no indication when the search might be suspended.

Coast Guard search planners calculated that by Sunday afternoon the most probable position of the missing airman was in an area 9.2 miles west of Tarague. The aircraft and cutter search patterns were concentrated in that area, while Guam police personnel searched along the shoreline.

All of those involved in the incident were deployed to Andersen from Minot Air Force Base, N.D., said an Andersen spokesman. McDonald was assigned to the 36th Expeditionary Aircraft Maintenance Squadron. The unit, along with six B-52 bombers, has been on Guam since September 2006 as part of Pacific Command’s continuous bomber rotation there.