Indonesian authorities closed an airport and residents left homes near an erupting volcano today due to the dangers of spreading ash, falling rocks, hot volcanic clouds and the possibility of a tsunami.

Mount Ruang on the northern side of Sulawesi Island had at least five large eruptions on Wednesday, causing the Centre for Volcanology and Geological Disaster Mitigation to issue its highest level alert, indicating an active eruption.

The crater emitted white-grey smoke continuously during the day on Thursday, reaching more than 500m above the peak.

People have been ordered to stay at least 6km from the 725m mountain. More than 11,000 people live in the affected area and were told to leave. At least 800 have done so.

An international airport in Manado city was temporarily closed on Thursday as volcanic ash was spewed into the air.

“We have to close flight operations at Sam Ratulangi Airport due to the spread of volcanic ash, which could endanger flight safety,” said Ambar Suryoko, head of the regional airport authority.

The volcanology centre noted the risks from the volcanic eruption include the possibility that part of the volcano could collapse into the sea and cause a tsunami. Tagulandang Island, east of the volcano, could be at risk if that occurred, and its residents were among those being told to evacuate.

“People who live in the Tagulandang Island area and are within a 6km radius must be immediately evacuated to a safe place outside the 6km radius, and especially those who live near the coast should be aware of the potential for incandescent rocks to erupt, hot clouds and tsunami waves that could be triggered by the collapse of a volcanic body into the sea,” Abdul Muhari, a spokesman for the National Disaster Mitigation Agency, said on Thursday.

The agency said residents will be relocated to Manado, the nearest city, on Sulawesi Island, a journey of six hours by boat.

Volcanic eruptions have triggered past tsunamis in Indonesia, including an 1871 eruption at Mount Ruang and the 2018 eruption of the Anak Krakatau volcano. Parts of the Anak Krakatau mountain fell into the ocean, causing a tsunami along the coasts of Sumatra and Java islands, killing 430 people.

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.