TOKYO - Three people have been confirmed dead after a medical transport helicopter crashed off Nagasaki Prefecture in southwestern Japan on Sunday, local media reported.

The death of an 86-year-old female patient, one of six people on board, was confirmed on the day of the incident, while a 68-year-old male family member accompanying her and a 34-year-old male doctor were pronounced dead on Monday, Kyodo News reported, citing the coast guard.

The emergency medical service helicopter took off from Tsushima Airport in Nagasaki Prefecture at 1:30 pm local time Sunday to transport a patient to a hospital in Fukuoka Prefecture. It was scheduled to arrive at 2:15 pm local time, but disappeared.

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At about 5:05 pm local time, a coast guard boat found the missing helicopter floating upside down and rescued three people alive and conscious. The other three passengers were also retrieved but later confirmed dead, the report said.

The helicopter is believed to have struck trouble when its tracker stopped moving around 1:43 pm local time, the report added.

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Local authorities took measures to prevent the helicopter from sinking and monitored it while working to determine the cause of the accident.