The search continues for survivors of the unexpected volcanic eruption of Mount Ontake on Saturday.

Dozens are presumed to be dead with authorities confirming that four of the 31 people rescuers found unconscious due to "cardiopulmonary" arrest at the peak have died, summarized ABC Net Au. The site further reported that more than 40 people have been injured, many of whom have broken bones.

Japan's NHK News per BBC wrote that the four who passed away were brought down the mountain Sunday and later on confirmed dead.

"We have confirmed that more than 30 individuals in cardiac arrest have been found near the summit," quoted The Guardian of a Nagano prefecture police spokesman who spoke to the AFP.

The mountain, with a height of 3,067-m, is popular among walkers, climbers and tourists. Mount Ontake erupted before noon, at a time when it drew many onlookers who were admiring the autumn view.

According to an official, per Reuters, "rescue efforts had been called off due to rising levels of toxic gas near the peak, as well as approaching nightfall" but have since resumed.

It was estimated that more than 250 people were trapped with plumes of ask, gas and rocks blanketed both the sky and nearby areas. The Guardian reported that by Sunday, local authorities had mobilized more than 500 people to conduct a massive search and rescue.

Of the hundreds trapped, most made their way down but there were about 40 who spent the night at the peak huddled together to keep warm.

BBC noted that there still remain 45 people unaccounted for, a number that includes those found near the summit. It is believed that others could be buried under volcanic ash. The exact locations of the bodies have yet to be determined.

Japan is one of the world's most seismically active nations. The last fatality was in 1991 when 43 people were killed in a pyroclastic flow at Mount Unzen, located in the south-western part of the country, in the Nagasaki Prefecture.

USA Today shared that Shinichi Shimohara, an on-site witness of the recent volcanic eruption, was on his way to work on Saturday. He claims to have heard a loud noise--sounding like strong winds and thunder, and then the volcano erupted.

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

This is the first major volcanic eruption for Mount Ontake since October 1979.