Thirty-one people were presumed dead on Sunday near the peak of a Japanese volcano that erupted a day earlier, catching hundreds of hikers unawares as it belched out clouds of rock and ash.
The deaths on Mount Ontake, 200 kilometers (125 miles) west of Tokyo, were the first from a Japanese volcanic eruption since 1991.
Police said the 31 were found in "cardio-pulmonary arrest", but declined to confirm their deaths pending a formal examination, as per Japanese custom.
Public broadcaster NHK and the Kyodo news agency later reported that four, all male, had been confirmed dead.
An official in the area said rescue efforts had been called off due to rising levels of toxic gas near the peak, as well as approaching nightfall.
Hundreds of people, including children, were stranded on the mountain, a popular hiking site, after it erupted without warning on Saturday, sending ash pouring down the slope for more than 3 kilometers (2 miles).
Most made their way down later on Saturday but about 40 spent the night near the 3,067 meter (10,062 feet) peak. Some wrapped themselves in blankets and huddled in the basement of buildings.
"The roof on the mountain lodge was destroyed by falling rock, so we had to take refuge below the building," one told NHK national television. "That's how bad it was."
More than 40 people were injured, several with broken bones.
Earlier, the Fire and Disaster Management Agency had said authorities were trying to confirm the whereabouts of 45 people.
It was not clear whether those 45 included the 31 people found in cardio-pulmonary arrest.
The volcano was still erupting on Sunday, pouring smoke and ash hundreds of meters into the sky. Ash was found on cars as far as 80 kilometers (50 miles) away.