A volcano on the remote Indonesian island of Halmahera erupted on Monday spewing a grey ash cloud six kms (four miles) into the sky, the country's volcanology agency said, adding it had issued a warning for aviation authorities managing local flights.

This follows a series of eruptions this month after authorities noticed an uptick of volcanic activity since April, leading to evacuations of people from seven nearby villages.

"The ash column is seen to be thick and grey and moving westward," the agency said, adding the eruption occurred at 3 a.m. local time (7 p.m. GMT) and recommending that a seven-km (4.35-mile) radius be cleared.

Footage shared by the agency on Monday showed the volcano spewing ash that grew thicker and eventually obscured it.

The agency also issued a "red" colour code warning to local aviation authorities on Monday, the highest of its kind due to ash exceeding six kms in height, its website stated.

It previously raised the alert level of the volcano to the highest on its scale on May 16.

Ibu's activities follow a series of eruptions of different volcanoes in Indonesia, which sits on the Pacific "Ring of Fire" and has 127 active volcanoes.

Flash floods and cold lava flow from Mount Marapi, one of the most active in West Sumatra province, covered several nearby districts following torrential rain on May 11, killing at least 62 people with 10 people still missing.

In recent weeks North Sulawesi's Ruang volcano has erupted, spewing incandescent lava. The eruption prompted authorities to evacuate more than 12,000 people on a nearby island.