Officials had warned the threat from the Mount Ruang stratovolcano in Indonesia’s outermost region was far from over after it sparked the evacuation of thousands when it stirred a spectacular mix of lava, ash columns and lightning last week.

But volcanic activity has since calmed at the crater and the country’s volcanology agency today lowered the alert level to the second-highest of a four-tier system.

“Based on the results of visual and instrumental monitoring which show a decrease in volcanic activity on Mt. Ruang, the status level… has been lowered from Level IV to Level III,” volcanology agency head Hendra Gunawan said in a statement.

The agency narrowed an exclusion zone from six to 4km.

Sam Ratulangi international airport in the provincial capital of Manado, more than 100km from the crater, reopened on Monday afternoon, authorities said.

It came after days of closures at the airport, where some airlines fly to Singapore, South Korea and China, because of volcanic ash.

More than 6,000 residents of neighbouring Tagulandang island, home to around 20,000 people, were evacuated outside the exclusion zone since the eruptions began, but no injuries or deaths were reported.

Indonesia, a vast archipelago nation, experiences frequent seismic and volcanic activity due to its position on the Pacific “Ring of Fire”.