TOKYO — Rescue workers have found at least 30 people unconscious and believed to be dead near the peak of an erupting volcano in central Japan, local government and police said Sunday.

Nagano prefecture posted on its website that about 30 people had heart and lung failure, the customary way for Japanese authorities to describe a body until police doctors can examine it. At least four of the victims were being brought down from Mount Ontake on Sunday afternoon, one day after the volcano erupted. Police later confirmed four people dead, according to Japan's national broadcaster NHK.

See also: 40 Injured and 7 Missing After Volcano Erupts in Japan

A Nagano police official described the number of unconscious people as more than 30. He spoke on condition of anonymity because he wasn't authorized to speak publicly.

Mount Ontake in central Japan erupted shortly before noon Saturday, spewing large white plumes of gas and ash high into the sky and blanketing the surrounding area in ash. The mountain is a popular climbing destination, and at least 250 people were initially trapped on the slopes, though most made their way down by Saturday night.

Before the unconscious victims were found, Japan's Fire and Disaster Management Agency said that 45 people had been reported missing. The exact location of the bodies and their identities were not immediately known.

Keita Ushimaru, an official in nearby Kiso town, said Nagano crisis management officials had informed the town that at least four people with heart and lung failure were being brought down to the town, and that there were others in the same condition. The journey was expected to take about three hours.

Rescue workers were also trying to help injured people and others who had been stranded on the mountain overnight, many taking refuge in mountain lodges. Some were unable to descend on their own, or unwilling to take the risk.

Military helicopters plucked seven people off the mountainside earlier Sunday, and workers were helping others make their way down the slopes. One woman was being carried on a stretcher, and a man with a broken arm was walking down.

Seven people were picked up in three helicopter trips, said Defense Ministry official Toshihiko Muraki. All are conscious and can walk, though details of their conditions were unclear, he said.

Japanese television footage showed a soldier descending from a helicopter to an ash-covered slope, helping latch on a man and then the two of them being pulled up.

The Self-Defense Force, as Japan's military is called, has deployed seven helicopters and 250 troops. Police and fire departments are also taking part in the rescue effort.

A large plume, a mixture of white and gray, continued to rise from the ash-covered summit of 3,067-meter (10,062-foot) Mount Ontake on Sunday, visible from the nearby village of Otaki. A convoy of red fire trucks with sirens blaring, as well as rescue workers on foot, headed past barriers into the restricted zone around the mountain.

Shinichi Shimohara, who works at a shrine at the foot of the mountain, said he was on his way up Saturday morning when he heard a loud noise that sounded like strong winds followed by "thunder," as the volcano erupted.

"For a while I heard thunder pounding a number of times," he said. "Soon after, some climbers started descending. They were all covered with ash, completely white. I thought to myself, this must be really serious."

Mount Ontake, about 210 kilometers (130 miles) west of Tokyo, sits on the border of Nagano and Gifu prefectures, on the main Japanese island of Honshu. The volcano's last major eruption was in 1979.

Additional reporting by Mashable