A group of hikers climbing Mount Mayon in the Philippines Mayon Volcano National Park engulfed in an ash cloud when the volcano unexpectedly erupted on Tuesday.

Five people have been confirmed dead and at least seven were injured, several in critical condition at a local hospital.

One of the guides from the ill-fated group said that the people killed were struck by rocks as large “as a living room”.

“It was so sudden that many of us panicked,” a local resident told AFP news.  “When we stepped out we saw this huge column against the blue sky.”

The Philippine Institute of Volcanology and Seismology called the eruption a “small phreatic event” that lasted just over a minute.  They said despite the eruption and the deaths of the hikers, no intensification of volcanic activity was observed.  Despite not raising the alert level in the region, they advised against entry into the 4 mile radius “Permanent Danger Zone” around the volcano.

The last eruption of was in late 2009 when local residents had to flee.