Search and rescue personnel combed Mount Marapi in Indonesia after a volcano erupted with dozens of hikers on its slopes. Five bodies have been recovered and an additional 18 are missing and expected to be found dead, authorities said on Tuesday.

There were 75 hikers on the mountain at the time of the eruption on Sunday, Abdul Muhari, head of communications at Indonesia’s disaster management agency, said in a briefing. Ongoing volcanic activity hampered rescue operations, but about 50 have been brought down alive for medical care, Indonesian national newspaper Kompas reported.

Mount Marapi, located in West Sumatra province and one of Sumatra island’s most active volcanoes, erupted for 4 minutes and 41 seconds, spewing ash 9,800 feet upward, which rained down on the surrounding area, Indonesia’s disaster management agency said.

It had been showing increased volcanic activity since January, when it had a smaller eruption, the agency said. On Nov. 16, it was assessed at an alert level which meant tourism was not recommended within two miles of the peak, the agency added.

It previously erupted in 1830 and in 1979, when about 60 were reportedly killed. Between 2011 and 2014 it spewed ash for several years before erupting. Indonesia, a Pacific island chain located in the “Ring of Fire” formed by tectonic plates, is one of the world’s most volcanically active nations.

correction

A previous version of this article misspelled the name of the head of communications at Indonesia’s disaster management agency. He is Abdul Muhari. The article has been corrected.