According to the Japanese NHK news outlet, citing police, the avalanche erupted at 10 a.m. local time (01:00 GMT) from Mount Norikura, standing on the border between Nagano and Gifu prefectures.
It hit some of the people who were skiing on the slope, leaving one person unconscious and others injured.
The media outlet said that the area of the snow that had collapsed from the mountain was some 200 meters (0.12 miles) wide and 300 meters long.