One man was killed and at least 11 people injured, some critically, when rocks from an erupting volcano rained down on skiers at a mountain resort in central Japan on Tuesday and an avalanche soon after the eruption engulfed about a dozen skiers.

Seven of those struck by rocks were members of Japan's Ground Self Defence Force (SDF) engaged in winter training manoeuvres, the Ministry of Defence said in a statement.

All were rescued, with one dying later, it added.

Japanese media said at least 12 people were injured, many apparently hit by volcanic rocks. Two were critically injured and three seriously, national broadcaster NHK said.

One person was trapped in the avalanche for some time before being dug out by rescuers, who included SDF members.

Kusatsu-Shirane, a 2,160-metre volcano, erupted on Tuesday morning, the Japanese Meteorological Agency (JMA) said. The agency warned that further eruptions could not be ruled out and that rocks could be thrown as far as 2 km from the peak.

Video footage from the top of the resort's gondola showed skiers gliding down the slopes as black rocks plummeted from the skies and snow billowed up as they struck the ground, sometimes just missing skiers. A cloud of black smoke later drifted in.

The resort temporarily lost power, leaving a number of skiers suspended in gondolas for around half an hour until they resumed moving. About 80 skiers, including some non-Japanese at a hut at the top of the mountain, were later rescued by helicopters on Tuesday afternoon.

It was unclear whether the avalanche was caused by the volcanic activity but they occurred nearly simultaneously.

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