Mount Lewotobi Laki-Laki on the tourist island of Flores erupted shortly after midnight, sending an ash cloud 1.2 kilometres (0.7 miles) above its peak, Indonesia's volcanology agency reported.

The volcano erupted once more at 09:36 am (0136 GMT), the agency said.

The latest rumblings follow authorities on Sunday evening raising the alert level of the 1,584-metre (5,197-foot) twin-peaked volcano to the highest in the country's four-tiered system.

"Lewotobi Laki-Laki's activities are still high," Indonesia's geological agency head Muhammad Wafid warned Sunday.

"The potential for a larger eruption than before can occur," he said in a statement.

A series of eruptions on Sunday spewed ash as high as six kilometres above Laki-Laki's peak, according to the volcanology agency.

Wafid urged residents to wear face masks to protect themselves from volcanic ash, while telling people not to carry out any activities at least six kilometres from the crater.

The geological agency chief also warned of the possibility of hazardous lahar floods -- a type of mud or debris flow -- if heavy rain occurs, particularly for communities around rivers that originate at the volcano's peak.

In November, Mount Lewotobi Laki-Laki erupted multiple times, killing nine people, cancelling scores of international flights to Bali and forcing the evacuation of thousands.

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".