One of the hikers on Mount Ontake in central Japan took this stunning video of the enormous ash cloud that came rolling down around him and hundreds of others when the mountain's volcano unexpectedly erupted just before noon local time on Saturday. As the New York Times is reporting, at least 31 people are believed dead in the wake of the eruption, while hundreds of other hikers managed to make it to safety.

The seriously scary video shows a small group on the side of the mountain sounding fairly confused at what they were seeing at first, and then almost calmly making their way down as the ash cloud envelops them.

As NPR notes, the mountain is a popular tourist destination at this time of year "where a relatively gentle slope and mountainside lodges draw visitors who want to take in views of the fall foliage."

According to an NPR correspondent in Japan, the last eruption at Mount Ontake was seven years ago, but the Times says the most recent eruption was in 1991. Seismologists apparently messed up big this time, having noted many small earthquakes in the vicinity in recent weeks but "nothing that [they] had interpreted as a warning that a major event was on the way."

The number of dead or injured remains uncertain, with a local source saying that as many as 45 people are still stranded on the mountain, and some who took shelter on the mountain's slopes are still, reportedly, conscious and getting rescued by emergency responders.

Below, more footage from Kyodo News.

Update: The death toll had risen to 36 as of Monday, and the injured number 59, including 27 with serious injuries. Also, as the AP reports, this was in fact the first fatal eruption of Mount Ontake in modern times. "An eruption occurred in 1979, but no one died."