Nine people died on 2,141-meter Mount Tomuraushiyama and another person perished on 2,052-meter Mount Bieidake, both in the Taisetsuzan range near here, police said.
The victims apparently died of exhaustion and hypothermia after winds of up to 90 kph, coupled with rain, lashed the area, lowering their body temperatures.
Survivors of a group on Tomuraushiyama said their guides had decided to continue the trek despite strong winds Thursday morning.
“Are we really going to be all right in this?” survivor Shinsuke Toda, 65, from Aichi Prefecture, said he wondered when they left a shelter for the peak.
A few hours later, one member of his group of 18 collapsed, followed soon by others, he said. He urged them to “get up or you’ll die.”
According to police, five members of the group, including Toda, managed to make their way down to safety. Thirteen others were airlifted by helicopter Friday morning; eight were later confirmed dead, including guide Hiroshi Kikkawa, 61. Six were women.
Separately, another man, apparently climbing the mountain alone, was found dead near its peak.
On Mount Bieidake, where a six-member party caught by the foul weather sought help Thursday, Atsuko Onoue, 64, from Hyogo Prefecture, was confirmed dead early Friday.
Hokkaido police are investigating the tour companies on suspicion of professional negligence resulting in deaths.
Both tours, connecting several peaks in the mountain range, are regarded as courses for experienced hikers, who must stay in unmanned shelters or tents at night.