One man was killed and at least 11 people were injured, some critically, when rocks from an erupting volcano rained down on skiers at a mountain resort in Japan, and an avalanche, possibly triggered by the eruption, engulfed about a dozen skiers. Video shows a cloud of volcanic ash moving ominously down the slopes of Mount Kusatsu-Shirane, followed some time later by a wall of snow engulfing the skiers.

Japan volcano ski resort avalanche
The cable car station where skiers were awaiting rescue, and the volcano that erupted are seen from a Kyodo News helicopter Kyodo/Reuters

Seven of the skiers were among 30 members of Japan's Ground Self Defence Force (SDF) who were participating in winter training manoeuvres, when they were buried by the avalanche about a half hour after the volcanic eruption, fire department and defence officials said.

Defence Minister Itsunori Onodera told reporters that the seven people trapped by the avalanche at the ski resort on the side of the 2,171-metre (7,122-foot) -high active volcano, were all rescued, but the soldiers were seriously injured. A 49-year-old male soldier who suffered broken bones died later, said Wataru Tatsukawa, an official at the regional military training camp.

Town officials said they believe everybody has been accounted for. Five civilian skiers suffered serious injuries such as broken bones, but none of the injuries were life-threatening, said a regional fire department official, Hayato Tobe. An earlier report that one or two people had been injured by shattered glass when rocks struck a gondola had not been confirmed. A rest house at the resort was hit by volcanic rocks, but the extent of damage was not known, resort official Yasuaki Morita said.

The crater had been off-limits because of low-level volcanic activity before Mount Kusatsu-Shirane erupted with rocks and ash around 10am. The Japan Meteorological Agency has since banned access to the mountain, and a large swathe of the snow-covered volcano is now covered by dark grey ash.

Japan volcano ski resort avalanche
Aerial view of a ski slope covered in snow and volcanic ash from the eruption of Mount Kusatsu-Shirane Kyodo/Reuters

The agency said the eruption and the avalanche could not be linked immediately. Snow conditions and seismic activity are some of the potential causes of an avalanche. The ski area's gondola was suspended after the eruption and about 80 skiers took refuge at a gondola station at the top of the ski slope, according to Tobe, the fire department official. A military helicopter was deployed to airlift the skiers to safer ground.

Kusatsu-Shirane last erupted in 1983. Japan sits on the Pacific "Ring of Fire" and is prone to earthquakes and volcanic eruptions.