Mount Lewotobi Laki-Laki, a 1,584-metre-high twin-peaked volcano on the tourist island of Flores, erupted at 11:05 am local time (0305 GMT), the volcanology agency said in a statement.

"An eruption of Lewotobi Laki-Laki Volcano occurred... with the observed ash column height reaching approximately 18,000 m above the summit," the agency said.

It 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.

Last month dozens of flights to and from Bali were cancelled after the volcano erupted. Volcanic 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.

There were no immediate reports of cancelled flights after Monday's eruption.

Laki-Laki, which means man in Indonesian, is twinned with the calmer but taller 1,703-metre (5,587-foot) 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".