Indonesian rescuers raced to evacuate thousands of people Thursday after a volcano erupted five times, forcing authorities to close a nearby airport and issue a warning about falling debris that could cause a tsunami.

Mount Ruang's crater flamed with lava against a backdrop of lightning bolts overnight after erupting four times on Wednesday, pushing an ash column more than a mile into the sky and forcing authorities to raise its alert level to the highest of a four-tiered system.

Taka, a local fisherman who only gave one name, was at sea helping people to safety by boat when the crater unleashed a fiery orange column.

"There was a mix of fire and rocks. Lava flowed in various directions," he told AFP.

The volcano, which sits on a remote island in Indonesia's outermost region with a peak 725 meters above sea level, was still billowing a column of smoke up to 800 meters (2,625 feet) high on Thursday morning, officials said.

Houses on the neighbouring remote island of Tagulandang were riddled with holes from falling volcanic rocks on Thursday, rescuers said, and residents were preparing to leave at least temporarily.

"The current condition, particularly the road condition, is covered by volcanic material," local rescuer Ikram Al Ulah told AFP by phone from the Tagulandang seaport.

"Currently, many people are still wandering around. Maybe to evacuate precious goods from their house."

There were no reports of deaths or injuries but authorities said they were rushing to evacuate more than 11,000 residents from the area around Tagulandang, home to around 20,000 people.

'People scattered'

Some residents were already trying to flee in a panic, according to officials.

"People evacuated on their own but without direction due to the volcano's eruption and... small rocks that fell," local search and rescue agency official Jandry Paendong said in a statement Thursday.

"The people scattered to find evacuation routes."

He said 20 staff were helping evacuate residents along the coastline near the volcano on rubber boats.

Authorities also evacuated a prison on Tagulandang island, ferrying 17 inmates along with 11 officials and 19 residents by boat to Likupang seaport in northern Sulawesi island, according to Ikram.

The evacuation was requested by the prison chief because the facility sits directly across from the volcano, said the rescuer.

Tourists and residents were warned to remain outside a six-kilometre exclusion zone.

More than 800 people were initially taken from Ruang to Tagulandang after the first eruption on Tuesday evening, before four more eruptions on Wednesday prompted evacuations from that island.

Tsunami warning

Authorities also warned of a possible tsunami as a result of the eruptions. 

"The communities in Tagulandang island... (need) to be on alert for the potential ejection of incandescent rocks, hot clouds discharges and tsunami caused by the collapse of the volcano's body into the sea," volcanology agency head Hendra Gunawan said in a statement Wednesday.

The authorities' fears were compounded by previous experience. 

In 2018, the crater of Mount Anak Krakatoa between Java and Sumatra islands partly collapsed when a major eruption sent huge chunks of the volcano sliding into the ocean, triggering a tsunami that killed more than 400 people and injured thousands.

Indonesia, a vast archipelago nation, experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire", an arc where tectonic plates collide that stretches from Japan through Southeast Asia and across the Pacific basin. 

The impact of Mount Ruang's eruption led to the closure of Sam Ratulangi International Airport in Manado city, located more than 100 kilometres (62 miles) from the volcano, for 24 hours until Thursday evening before being extended to midnight.

The airport runways in Manado were shut "due to the spread of volcanic ash which could endanger flight safety", Ambar Suryoko, head of the Manado region airport authority office, said in a statement. 

The airport hosts airlines that fly to Singapore and cities in South Korea and China.

Budget airline AirAsia also cancelled flights to and from nine airports in eastern Malaysia and Brunei until Friday morning due to the Ruang eruption, it wrote on social media platform X.

The volcano's last major eruption was in 2002, causing damage to nearby settlements and also requiring the evacuation of residents.

Locals this time around expressed their shock on social media.

One posted video showed a swarm of electricity coming from multiple lightning bolts as lava shot into the air.

"Oh God! Oh God! Oh God!" a man is heard saying.