A medical transport helicopter carrying a patient fell into the sea in southwestern Japan Sunday, leaving three of the six people aboard dead, the Japan coast guard said.

Axar.az reports citing AP, the pilot, Hiroshi Hamada, 66; Kazuto Yoshitake, a helicopter mechanic and a 28-year-old nurse, Sakura Kunitake, were rescued by the coast guard earlier in the day after they were found in the waters clinging to inflatable lifesavers near the capsized helicopter.

The three suffered hypothermia, as their body temperatures dropped abnormally, but were conscious, an official with the coast guard told The Associated Press, speaking on condition of anonymity in line with regulations.

The bodies of medical doctor, Kei Arakawa, 34; Mitsuki Motoishi, 86, the patient, and her caretaker Kazuyoshi Motoishi, 68, were later recovered by a Japan Air Self-Defense Force helicopter. Their hearts had stopped, and they were later confirmed dead by a physician.

The coast guard deployed two planes and three ships to the area as part of the rescue operation.

The six people were aboard what the Japanese call “a doctor helicopter,” on their way to a hospital in Fukuoka from Tsushima airport in Nagasaki Prefecture, when it crashed, according to the coast guard. It left Tsushima at 1:30 p.m.

The cause of the accident remains under investigation, the coast guard said Monday.