Around 50,000 people have been evacuated from their homes near an active volcano in Indonesia’s Bali, The Guardian reported on Monday. Indonesian authorities have imposed a 12-kilometre exclusion zone around the crater Mount Agung, which experienced increased volcanic activity on Sunday.

“The latest analysis indicates that Mount Agung’s seismic energy is increasing, and has the potential to erupt,” Reuters reported Indonesia’s National Vulcanology Center as saying. “However, no one can predict exactly when there will be an eruption.”

There have been tremors since August, and the volcano on the tourist island is threatening to erupt for the first time in 50 years. It last erupted in 1963, killing more than 1,000 people.

Authorities have arranged makeshift shelters in town halls, school gymnasiums and set up tents in villages around the volcano to house thousands of evacuees. “The biggest challenge is we can’t predict the number of evacuees,” said Putu Widiada, head of the local disaster management agency in Klungkung district. “If the number of evacuees exceeds our maximum capacity, we have asked that every public hall in the district be prepared to become evacuation camps.”

Indonesia has nearly 130 active volcanoes along the Pacific ring of fire, which is more than in any other country.