The unexpected eruption of Mount Moto-Shirane in Gunma Prefecture halted ski lift operations, leaving around 80 people, including tourists from Taiwan and Britain, temporarily stranded in a restaurant near the top of the mountain.

A Meteorological Agency official said observational data had not indicated heightened volcanic activity, highlighting the difficulty of issuing disaster alerts in a nation prone to volcanic eruptions and earthquakes.

Around 30 Ground Self-Defense Force troops of the 12th Brigade, well known for being sent to areas affected by natural disasters, were engaging in ski training in the area at the time. According to the GSDF and the Defense Ministry, a 49-year-old male GSDF member died and seven other troops were injured, with two in serious condition.

Separately, stones from the eruption of Mount Moto-Shirane, which is part of Mount Kusatsu-Shirane, hit a gondola lift and injured at least four people on board with shattered glass, according to local rescuers. The 9:59 a.m. eruption of the 2,171-meter mountain is the first since 1983, according to the Meteorological Agency.

The stones also crashed through the roof of a rest house where about 100 people had evacuated, the rescuers said.

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.

“I was scared to death,” said a 71-year-old man from Tokyo, who was riding in the gondola, recalling how two stones smashed the windows. He said the lift was halted for about 30 minutes.

A 52-year-old woman said she heard a bang when she was on a slope near the peak. She crawled toward the gondola station as the mountain spewed cinders, and took shelter in the basement there for about an hour.

“I thought I was going to die,” she said.

Chief Cabinet Secretary Yoshihide Suga said at an afternoon news conference that the government had not seen reports of additional casualties or missing people.

Tokyo Electric Power Company Holdings Inc. said a power outage occurred near the ski resort after the eruption.

Following the eruption, the weather agency raised the volcanic alert status from 1 to 3 — on a scale of 5 — a level that restricts entry to the mountain, while warning of large amounts of ash in the area.

It also urges the elderly, children and others in need of aid during evacuations to begin preparations to leave the area.

Plume conditions remain unknown due to bad weather, but the agency said it is unlikely that deposits of ash will reach the nearby Kusatsu hot spring resort and residential areas.

The central government has set up a liaison office at the Prime Minister’s Office to gather information on the eruption, while Gunma’s governor requested the dispatch of the GSDF. The mountain is located near the border of Gunma and Nagano prefectures and is one of 50 volcanic mountains continuously monitored by the Meteorological Agency.