Japan's Mount Ontake volcano erupted without warning on Saturday, sending plumes of heavy, toxic volcanic ash and rock into the air, and causing embers to fall nearly two miles from its crater.

So far, 12 victims have been retrieved from the mountain, identified, and confirmed dead. Today, Nagano Prefecture Police said that 24 bodies remain on the slopes of the volcano, bringing the suspected death toll to at least 36.

More than 500 rescuers returned to the scene today. It is not yet clear how the victims died, but asphyxiation from poisonous gases is common in eruptions of this kind. This helicopter footage shows the ongoing rescue mission.

This video of the huge ash cloud created by the eruption is from Japan's Ministry of Land, Infrastructure, and Transport.

About 250 people were trapped on the slopes of the popular hiking spot, but the majority scrambled down to safety, like Kuroda Terutoshi, who caught the eruption on camera.

At 38 seconds into this chilling amateur footage, which has since gone viral, you see the cloud sweep over the hikers. A film of ash around 20 inches thick covered much of the mountain.

Mount Ontake lies about 125 miles west of Tokyo and, at 10,062 feet, is the second-highest volcano in Japan.

"All of a sudden ash piled up so quickly that we couldn't even open the door," Shuichi Mukai, who worked in a lodge just below the summit, told Reuters.

"We were really packed in here, maybe 150 people. There were some children crying, but most people were calm. We waited there in hard hats until they told us it was safe to come down." Hiking active volcanoes is a popular and normal pastime in Japan, according to BBC correspondent Rupert Wingfield-Hayes.

Footage shows tricky rescue operation near Japan volcano after 30 lifeless hikers were found — BBC News (World) (@BBCWorld)September 28, 2014

Saturday's eruption released super hot steam and ash, rather than lava from the magma chamber, as explained in National Geographic. This is known as a "phreatic" eruption, which is more difficult to predict but a less dangerous type of eruption than those where molten rock is present.

Ontake also belongs to a class of "stratovolcanoes," known for unpredictable eruptions, which form where one continental plate is pushed beneath another.

Japan is one of the world's most seismically active nations. The country has over 100 active volcanoes and accounts for about 10 percent of all active volcanoes in the world. Despite an average of 10 eruptions a year, there have been no deaths from volcanic activity in Japan since 1991, when 43 people died at Mount Unzen in the southwest of the country.