The volcano alert for Bali’s Mt Agung has been raised to the highest level, with fears of a major eruption imminent.

The Indonesian National Board for Disaster Management said the state of the volcano alert has been raised from level 3 to level 4. It has urged people within a 10km radius of Mt Agung to evacuate. The exclusion zone around the volcano was previously a 6km radius.

All flights from Australia to Bali have been cancelled as ash from Mt Agung fills the skies.

Lombok International Airport has been closed since Sunday and more than 400 flights have been cancelled.

Pak Kasbani, head of the Indonesian Centre for Volcanology and Geological Hazard Mitigation, said the alert was raised at 6.00am (local time) because the eruptions had changed from steam-based to magmatic in nature.

The airport is expected to be closed for 18 hours and reassessed after this period.

“We don’t expect a big eruption but we have to stay alert and anticipate,” Kasbani added.

The Department of Foreign Affairs and Trade has told Australians currently in Bali to “plan for the possibility that you won’t be able to depart Bali on your scheduled flight”.

When Mt Agung last erupted in 1963 it killed more than 1,000 people and razed several villages.