Japan’s second highest volcano Mount Ontake erupted on Saturday, leaving hundreds of people trapped on the mountain for hours and more than 30 feared dead.

Located in central Japan, 3,067-metres-high Mount Ontake is a popular location for walkers and climbers, Reuters reported.

According to Japan Times, it erupted at around noon. The eruption was reportedly a phreatic one, caused by groundwater overheated by magma. The water then exploded into steam that pulverized large amounts of rocks inside the volcano conduit. The rocks erupted together with white plumes of gas and ash, rising approximately 4 kilometers into the sky, Volcano Discovery reported.

Following the eruption, hikers and residents were warned of falling rocks and ash within a radius of 4 kilometers, Japan Times said.

According to Reuters, more than 40 people were also injured, several with broken bones.

Last major eruption of Mount Ontake happened in 1970, when according to Discovery News, it expelled more than 200,000 tons of ash.

Volcanoes erupt periodically in the country but as Reuters reported there have been no fatalities since 1991, when 43 people died in a pyroclastic flow at Mount Unzen in southwestern Japan..