Police in central Japan say they have found bodies of 31 hikers near the summit of Mount Ontake, a volcano that erupted without warning on Saturday, spewing ash, rocks and steam.
Officials confirmed four deaths while 27 others were described as being in a state of "cardiac arrest," a term Japanese authorities often use to describe the dead until doctors can examine the body.
More than 550 Japanese police, firefighters and military troops ascended the slopes of 3,067-meter (10,121-foot) Mount Ontake Sunday, searching for survivors and casualties from the eruption.
Rescue workers endangered
However, rescue efforts were called off mid-afternoon Sunday because toxic volcanic gases were building and it was becoming too dangerous for emergency workers, an official at the Nagano prefectural government told the French news agency AFP.
"The rescue team suspended their operation because of the increasing concentration of sulphurous gas in the area," the official said.
A suffocating blanket of ash up to 20 centimetres (eight inches) deep covered a large area of the volcano, and had forced up to 150 to seek refuge in mountaintop shelters at one point.
Local officials believe 45 to 49 people sheltered overnight in cabins on the mountain, although details remained unclear. NHK News, Japan’s national broadcaster, reported the stranded hikers were expected to try descending Sunday.
Popular autumn spot
The mountain is popular among walkers, particularly in late September when the turning of the autumn leaves makes for dramatic scenery.
Officials said one person was rescued from under a thick layer of ash, and other hikers were seriously injured.
However, AFP and The Associated Press reported that emergency helicopters rescued seven people, including two who were able to wave at a Self Defense Force helicopter.
Some were unable to descend on their own, or unwilling to take the risk, AP reported.
The volcano, which sits on the border of Nagano and Gifu prefectures west of Tokyo, had its last major eruption in 1979.
“It was like thunder,” a woman told public broadcaster NHK of the first eruption at the volcano in seven years. “I heard boom, boom, then everything went dark.”
Hikers who descended from the volcano reported scenes of horror, with stones raining down and hot ashes filling the air, AFP reported.
Video footage shot inside a cabin, taken shortly after the eruption and shown on NHK, revealed the screams of terrified hikers as rocks thundered against the roof and walls.
Tokyo's Haneda airport said incoming domestic flights were experiencing delays of about 40 to 50 minutes because they were forced to change routes. International flights to and from Haneda were not affected by the eruption, the airport said.
Prime Minister Shinzo Abe, who returned from the United States on Saturday, said he had ordered the military to help in rescue efforts.
“I instructed to do all we can to rescue the people affected and secure the safety of the trekkers,” Abe told reporters.
Kiso Prefectural Hospital, near the mountain, said it had dispatched a medical emergency team.
“We expect a lot of injured people so we are now getting ready for their arrival,” said an official at the hospital.
Mari Tezuka, who works at a mountain hut for trekkers, told Reuters: “It's all white outside, looks like it has snowed. There is very bad visibility and we can't see the top of the mountain.
“All we can do now is shut up the hut and then we are planning on coming down... This is a busy season because of the changing autumn leaves. It's one of our busiest seasons," Tezuka said.
The Japan Meteorological Agency warned people to stay away from the mountain, saying hot debris could fall within a four-kilometer radius.
Some material for this report came from Reuters, AP and AFP.