A volcano in eastern Indonesia spewed a colossal ash tower into the sky on Tuesday, authorities said, after they raised its alert level to the highest of a four-tiered system.

Mount Lewotobi Laki-Laki, a 1,584-metre-high twin-peaked volcano on the tourist island of Flores, erupted at 5.35pm Hong Kong time, the volcanology agency said in a statement.

"The height of the eruption column was observed at approximately 10,000 metres above the summit. The ash column was observed to be grey with thick intensity," it said, after the alert level was raised.

There were no immediate reports of damage or casualties.

Geology agency head Muhammad Wafid said residents and tourists should avoid carrying out any activities within at least seven kilometres of the volcano's crater.

But he 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.

He also urged residents to wear face masks to protect themselves from volcanic ash.

In November, Mount Lewotobi Laki-Laki erupted multiple times, 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 Tuesday's eruption. (AFP)