BALI, Indonesia – More than 57,000 people have fled the surrounds of Mount Agung volcano on the Indonesian tourist island of Bali, fearing an imminent eruption, officials said Tuesday.

An increasing frequency of tremors from the volcano indicates magma is continuing to move toward the surface and an eruption is possible, said National Disaster Mitigation agency spokesman Sutopo Purwo Nugroho. He said more than 560 volcanic earthquakes were recorded on Monday, most of them shallow.

The alert status of Agung was raised to the highest level on Friday following a dramatic increase in seismic activity. It last erupted in 1963, killing about 1,100 people.

READ MORE: Bali volcano warning: Here’s what tourists should know about Mount Agung

Another disaster agency official, Waskita Sutadewa in Bali, said people have scattered to all corners of the island and some have crossed to the neighbouring island of Lombok. The evacuees are living in temporary shelters, sports centres, village halls and with relatives or friends. Some return to the danger zone, which extends up to 12 kilometres (7.5 miles) from the crater, during the day to tend to livestock.

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Officials have said there’s no immediate threat to tourists, but some are already cutting short their stays in Bali. A significant eruption would force the closure of Bali’s international airport, stranding thousands.

“It’s obviously an awful thing. We want to get out of here just to be safe,” said an Australian woman at Bali’s airport who identified herself as Miriam.

Nugroho said hundreds of thousands of face masks will be distributed in Bali as part of government humanitarian assistance that includes thousands of mattresses and blankets.

“The chances of an eruption are very high, but we cannot be sure when it will erupt,” he said at a news conference in the capital, Jakarta.

He said not everyone had left the danger zone because they didn’t want to leave livestock, were underestimating the risk or because of religious reasons.

“Officers continue to sweep the area and are appealing for people to evacuate,” he said.

In 1963, Agung hurled ash as high as 20 kilometres (12 miles) and remained active about a year. Lava travelled 7.5 kilometres (4.7 miles) and ash reached Jakarta, about 1,000 kilometres (620 miles) away.

The mountain, 72 kilometres (45 miles) to the northeast of the tourist hotspot of Kuta, is among more than 120 active volcanoes in Indonesia.

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The country of thousands of islands is prone to seismic upheaval due to its location on the Pacific “Ring of Fire,” an arc of volcanoes and fault lines encircling the Pacific Basin.