The single-propeller plane with four people on board plunged into Japan's Northern Alps in Tateyama yesterday, police said.
Police received an emergency call from a man believed to be one of the four people - all men aged from 21 to 57 - on board the small plane, they said.
"Two people, including the captain, are unconscious and the remaining two others are stuck but conscious," a Toyama prefectural official had told AFP yesterday after they received the distress call.
It was fourteen hours after the distress call when rescuers finally spotted the aircraft on the snowy mountain slope at a height of about 2,300 metres (7,545 feet), police and reports said.
The four men were then taken to hospital where they were confirmed dead, police said.