At least 12,000 people were being evacuated and multiple airports shut Wednesday after Indonesia's Mount Ruang volcano erupted, spewing ash and rocks.

Mount Ruang, located in the Sangihe Islands arc in North Sulawesi province, has been increasingly active in recent weeks.

Authorities on Tuesday raised the alert level to the highest possible after new eruptions, warning of potential pyroclastic flows, deadly ash surges and the possibility of tsunami.

The eruption also caused a power outage on neighbouring Tagulandang island and forced the closure of Sam Ratulangi International Airport in Manado, disrupting air travel in the region, officials said.

"A total of around 6,500 people have been evacuated from five districts," Feri Ariyanto, a search and rescue official in Manado city, told dpa.

Abdul Muhari, the spokesman for the National Disaster Management Agency, said 12,000 residents who live within a 7-kilometer (4.35 miles) radius around the volcano would have to be evacuated.

He said residents were being evacuated by ferries operated by the National Search and Rescue Agency, the Indonesian navy and police.

"We will ensure that they are prohibited from leaving the evacuation shelters to return home during the extended emergency response period of up to 14 days, or until conditions are completely normal," he said in a statement.

Residents of Tagulandang were plunged into darkness following Tuesday's eruption, while the airports in Manado and Gorontalo remained closed, said Ariyanto.

"All power has been cut off," he said.

Ships provided the only source of illumination at the island's port, local media reported.

"We panicked as showers of volcanic rocks, gravel, and ash rained down," Yefti, a resident, was quoted as saying by medcom.id news portal.

The Indonesian archipelago sits on the seismically active "Ring of Fire" and is no stranger to volcanic eruptions and earthquakes.