“The Volcanic Ash Advisory shows that the plane routes have been covered by volcanic ash, this is dangerous for the flights,” Wisnu Darjono from the air traffic agency AirNav official said.

Some 40,000 people have abandoned their homes in the danger zone but as many as many as 100,000 would likely be forced to leave, disaster agency officials have said.

The exclusion zone around Agung, which is 75 kilometres away from the beachside tourist hub of Kuta, has also been widened to 10 kilometres.

As of late Monday some 445 flights had been cancelled, affecting more than 59,000 people travelling to Bali, a top holiday destination that attracts millions of foreign tourists every year.

The airport on nearby Lombok island - also a popular tourist destination east of Bali - closed on Sunday as ash headed in that direction, but reopened early Monday.

China said there were 17,000 Chinese tourists on Bali before the latest eruption of Mount Agung.

The Chinese consulate on the Indonesian island said on its website that airlines and travel services were arranging 100 buses to take tourists to catch ferries to neighbouring Java.

The Chinese foreign ministry issued a statement urging travellers to be “vigilant about safety” when deciding whether to visit Bali.

China Eastern Airlines, one of the country’s biggest carriers, canceled flights Sunday and said passengers due to fly any time between then and December 10 could obtain refunds.

Mount Agung last went off in 1963, killing some 1,600 people in one of the deadliest eruptions ever seen in a country with nearly 130 active volcanoes.

Memories of that disaster have helped drive people towards community centres and makeshift camps, including villagers who have to leave precious livestock behind.

“I am very worried because I have experienced this before,” 67-year-old Dewa Gede Subagia, who was a teenager when Agung last roared, said at one evacuation centre.

“I hope this time I won’t have to evacuate for too long. In 1963, I left for four months.”

Experts said however that Agung’s recent activity matches the build-up to that disaster which ejected enough debris - about a billion tonnes - to lower global average temperatures by 0.2 - 0.3 degrees Celsius for about a year.

“What we are seeing at the moment are small explosions, throwing out hot gases and fragments of molten rock, or ash,” said David Pyle, a volcano expert at the University of Oxford in Britain.

“The probability of a large eruption is high, but this may take some days or weeks to unfold.”

Agung rumbled back to life in September, forcing the evacuation of 140,000 people living nearby. Its activity decreased in late October and many returned to their homes.

However, on Saturday the mountain sent smoke up into the air for the second time in a week in what vulcanologists call a phreatic eruption - caused by the heating and expansion of groundwater.

Then on Monday so-called cold lava flows appeared - similar to mud flows and often a prelude to the blazing orange lava seen in many volcanic eruptions.

Indonesia is the world’s most active volcanic region. The archipelago nation with over 17,000 islands lies on the Pacific “Ring of Fire” where tectonic plates collide, causing frequent volcanic and seismic activities.

Last year, seven were killed after Mount Sinabung on the western island of Sumatra erupted, while 16 were left dead by a Sinabung eruption in 2014.

Additional reporting by Associated Press