TOKYO - A Singaporean woman and three companions who had gone missing while descending Hokkaido's tallest mountain Asahidake were found alive on Wednesday (Oct 18).

They were located at 5.45pm (4.45pm Singapore time), about 22 hours after making their first police report and after spending a night on the mountain without a tent as temperatures fell to below -7 deg C.

The four were found conscious along a stream about 1.5km from the mountain's ropeway station at about 1,600m above sea level.

The Singaporean woman, who is reported to be in her 20s, was with a Malaysian man, as well as an elderly Japanese couple.

The hikers were able to converse with emergency responders when they were found, Japanese public broadcaster NHK said, although the younger man was suffering from hypothermia.

Given their extreme fatigue, they were to spend the night on the mountain under the watch of rescuers, before making their way down on Thursday morning.

Some 130 personnel from the Hokkaido police force and from the military Ground Self-Defence Force (GSDF) were involved in the successful operation.

The 2,291m Asahidake is located in Higashikawa town in central Hokkaido.

The two couples had met while descending Asahidake, at a point near the mountain's seventh station at an elevation of about 1,930m.

But they took a wrong turn in the heavy snow and found themselves stranded.

The Japanese couple - Yokohama native Masahiko Kato, 71, and his wife Yumiko, 65 - had planned a day hike to the mountains starting from the ropeway station.

But they decided to make a U-turn near the eighth station when the weather took a bad turn. On their way down, they met the younger couple.

Mr Kato lodged a police report at about 7.35pm on Tuesday, saying that the four of them had taken a wrong turn and did not know where they were.

Ground emergency responders began an urgent search-and-rescue operation at about 3am on Wednesday, while a planned helicopter search had to be called off due to low visibility and thick fog.

At about 8.30am on Wednesday, Mr Kato called the police again and said all four were conscious and alive, although the young man "had difficulties moving due to hypothermia".

He added that they did not know where they were, and that they only had water but no food.

The Singaporean woman was also said to have made a separate police report.