Indonesian authorities issued a tsunami alert Wednesday after eruptions at Ruang mountain sent ash thousands of feet high. Officials ordered more than 11,000 people to leave the area.

The volcano on the northern side of Sulawesi island had at least five large eruptions in the past 24 hours, Indonesia’s Center for Volcanology and Geological Disaster Mitigation said. Authorities raised their volcano alert to its highest level.

At least 800 residents left the area earlier Wednesday.

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Indonesia, an archipelago of 270 million people, has 120 active volcanoes. It is prone to volcanic activity because it sits along the “Ring of Fire,” a horseshoe-shaped series of seismic fault lines around the Pacific Ocean.

Authorities urged tourists and others to stay at least 6 kilometers (3.7 miles) from the 725-meter (2,378 foot) Ruang volcano.

Officials worry that part of the volcano could collapse into the sea and cause a tsunami as in a 1871 eruption there.

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Tagulandang island to the volcano's northeast is again at risk, and its residents are among those being told to evacuate.

Indonesia’s National Disaster Mitigation Agency said residents will be relocated to Manado, the nearest city, on Sulawesi island, a journey of six hours by boat.

In 2018, the eruption of Indonesia's Anak Krakatau volcano caused a tsunami along the coasts of Sumatra and Java after parts of the mountain fell into the ocean, killing 430 people.