The aviation disruption came just weeks after the same rumbling volcano caused dozens of flight cancellations to and from the popular resort island.
Mount Lewotobi Laki-Laki, on the tourist island of Flores, erupted at 11.05am, the volcanology agency said.
“An eruption of Lewotobi Laki-Laki volcano occurred… with the observed ash column height reaching approximately 18,000m above the summit,” the agency said in a statement.
It forced the cancellation of 24 flights at Bali’s international airport, general manager Ahmad Syaugi Shahab said.
“Several airlines serving the routes to Labuan Bajo (on Flores), Australia, Singapore, and South Korea have confirmed cancellations and delays,” he said in a statement.
He said the airlines included Virgin Australia, Jetstar Airways and AirAsia Indonesia.
Despite some carriers cancelling flights, the airport manager said “the spread of volcanic ash has not affected the Bali airspace”.
Australia’s Jetstar said several flights were cancelled “due to volcanic ash caused by an eruption of Mount Lewotobi”.
‘Explosive eruptions’
The volcanology agency warned of the possibility of hazardous lahar floods – a type of mud or debris flow of volcanic materials – if heavy rain occurs, particularly for communities near rivers.
There were no immediate reports of damages or casualties.
The activity level at the volcano was “very high, marked by explosive eruptions and continuous tremors”, geology agency head Muhammad Wafid said in a statement.
He also urged residents to stay at least 6km away from the volcano and to wear face masks to protect themselves from ash.
Last month dozens of flights to and from Bali were cancelled after the volcano erupted.
Ash rained down on several communities around the volcano and forced the evacuation of at least one village.
Mount Lewotobi Laki-Laki erupted multiple times in November, killing nine people and forcing thousands to evacuate, as well as the cancellation of scores of international flights to Bali.
Laki-Laki, which means man in Indonesian, stands at 1,584m and is twinned with the calmer but taller 1,703m volcano named Perempuan, after the Indonesian word for woman.
Indonesia, a vast archipelago nation, experiences frequent seismic and volcanic activity due to its position on the Pacific “Ring of Fire”.