A Coast Guard sergeant suffered a stroke on Wednesday while taking part in the search for missing victims from the ferry disaster off Jindo, South Jeolla Province.
The sergeant, identified by his surname Chung, was involved in a radar operation in a rescue helicopter.
According to his colleagues, Chung complained of numb feet and dizziness after being relieved of his mission and fainted at 8:20 p.m.
He was taken by helicopter to a hospital in the nearby city of Mokpo and rushed into surgery after being diagnosed with a multiple cerebral hemorrhage.
An official from the Korea Coast Guard said chronic hypertension and overwork are presumed to be the cause.
Chung was sent to the scene Wednesday morning for two shifts instead of one due to a staff shortage.