The Japanese military has joined the search for a boy missing in the country's north after his parents abandoned him in a bear-inhabited forest as punishment.
Yamato Tanooka has been missing since Saturday after his parents said they made him get out their car on a mountain road as punishment for misbehaving.
He was reportedly left without food or water.
75 personnel from the Ground Self-Defence Force joined some 130 fire rescuers, police officers and volunteers to look for the seven-year-old, rescuer Satoshi Saito told AFP.
Yamato Tanooka.
Rescuers have admitted it is a frustratingly difficult task to find the vanished boy due to a lack of evidence found so far of his presence in the rugged mountainous area on the wild bear-inhabited island of Hokkaido.
The boy's parents originally told police their son had got lost while they were out hiking to gather wild vegetables, but later admitted they were angry and tried to punish him because he had thrown stones at cars and people.
The parents told police they returned after a few minutes to find him missing.
"We have done an unforgivable thing to our child and we have caused a lot of trouble for everyone," said Takayuki Tanooka, Yamato's father.
Yamato has been missing since Saturday. (AAP)
"I just hope he is safe."
On the northern side of the road where the boy is believed to have been abandoned is a slope of Mount Komagadake, which rises to an altitude of 1131 metres.
The local town of Nanae requested military support after rescuers and police officers had already scoured the area for four days, with heavy rains at times hampering the search.
"We asked the SDF to go into places which people can't easily access such as deep crevasses along creeks," town spokesman Mitsuru Wakayama told AFP.
"We have already covered the same areas over and over again," he said, but added that it is hard to imagine even a lost adult being able to travel over such an extensive area on foot.
His parents said they left him alone for a few minutes before returning to find him gone. (AAP)
"We have not taken such a long time before to find signs of a person in distress," he said.
