A medical helicopter crashed into the sea off the coast of Tsushima Island on Sunday, killing three of six people on board, including a patient being transported, the Japan Coast Guard said Monday.

At around 2:50 p.m. on Sunday, the 7th Regional Coast Guard Headquarters in Kitakyushu, Fukuoka Prefecture, received a report that the helicopter transporting the patient from Tsushima in Nagasaki Prefecture to a hospital in the city of Fukuoka had gone missing off the island's coast.

According to the regional coast guard headquarters, the helicopter was found floating belly-up on the sea east of Tsushima, and three survivors — a female nurse, a male pilot and a male mechanic — were seen clinging on to inflatable lifesavers.