It was not immediately clear how many of the victims were students, an official said, Joinfo.com reports with reference to Reuters.
The avalanche occurred on Monday morning near a ski slope in Nasu, 160 km (100 miles) north of Tokyo, where 52 high school students and 11 teachers were climbing, a local government official said.
The eight showed no vital signs, officials said.
Japanese officials typically do not declare victims dead until a doctor has made a formal announcement.
“We have avalanche incidents once or twice a year around here, but haven’t had anything this big,” a fire department official said.