The bodies of at least 12 hikers are believed to be lying somewhere on the still-smoldering Mount Ontake, a popular trekking destination that saw a spectacular eruption on September 27.
Rescue workers have already retrieved the bodies of 51 other victims, making it Japan's deadliest eruption for almost 90 years.
"The rescue efforts are suspended due to heavy rains in the area," said a disaster official at Nagano prefecture.
Phanfone, a Laotian term for "animal", was at noon (0300 GMT) located around 120 kilometres (75 miles) southeast of Yakushima, Kagoshima prefecture in southern Japan, according to the Japan Meteorological Agency.
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Packing gusts of up to 216 kilometres per hour, the typhoon was moving north at speed of 20 kilometres per hour, and could make landfall by tomorrow, the agency said.
Gasses are still rising from the mountain, now covered by a knee-deep layer of wet and sticky ash that has hampered with the search-and-rescue operation.
Mount Ontake was popular among hikers particularly as the autumn leaves turn their colours.