President Moon Jae-in on Friday expressed deep condolences after two Coast Guard officials were killed in a helicopter crash earlier in the day, Moon's spokesperson said.

Moon also called for utmost efforts to find one missing crew member of the helicopter and wished for the recovery of another crew member who was rescued, presidential spokesperson Park Kyung-mee said in a statement.

Four people were aboard the Sikorsky S-92 helicopter when it went down in waters 370 kilometers southwest of Mara Island at 1:32 a.m., according to Coast Guard officials.

The crash happened shortly after the helicopter took off to return to Busan after dropping off six Coast Guard rescuers on the patrol boat that was on its way to help with rescue operations for crew members missing from a tug boat in waters near Taiwan.

Moon instructed relevant authorities to closely cooperate with Taiwan for rescue operations for the missing crew members, Park said. (Yonhap)