Kusatsu-Shirane, a 2,160-metre volcano located northwest of Tokyo, erupted on Tuesday, triggering an avalanche and trapping skiers.
Footage from the top of the resort’s gondola shows rocks hurl out of the erupting volcano and crash down onto the ski slopes.
A column of black smoke is seen spewing from the volcano as it erupted on Tuesday morning.
A number of people are expected to have been caught in the avalanche, around 10 people have been injured and a member of Japan’s self-defence forces has died.
Japan’s Meteorological Agency (JMA) confirmed that Mount Kusatsu-Shirane erupted early on Tuesday at around 10:00am local time.
A JMA official told Reuters: “Based on various measurements, we can say that the mountain appears to have erupted, but we are still trying to confirm facts on the ground.”
Around 80 skiers were trapped at a gondola station at the top of the mountain awaiting rescue, according to fire department official Hayato Tobe.
The resort temporarily lost power, leaving a number of skiers suspended in gondolas for around half an hour until they resumed moving.
One skier told NHK: “There was this huge boom, and a big plume of totally black smoke rose up.
“I had absolutely no idea what had happened.”
Mount Kusatsu-Shirane is located near the border of Gunma and Nagano and remains constantly observed by the Meteorological Agency.
Japan is located on the Ring of Fire, a huge area in the basin of the Pacific Ocean where earthquakes and volcanic eruptions frequently occur.