Indonesian authorities at Bali's international airport were fighting Monday to clear a backlog after almost 900 flights were cancelled or delayed in recent days due to a volcanic eruption, causing travel chaos during the peak holiday season.

Mount Raung on Indonesia's main island of Java, which has been rumbling for weeks, sent an ash cloud floating over Bali on Thursday, forcing the airport to close for two days.

Thousands of tourists who were visiting the resort island famed for its palm-fringed beaches found themselves stuck at Ngurah Rai airport, near Bali's capital Denpasar, anxiously watching departure boards, sitting and sleeping on the floor.

The airport closed again on Sunday as the ash returned but reopened several hours later after authorities gave the all-clear.

Officials said the clouds of ash continued to drift away from Bali Monday, giving airport authorities a chance to clear the backlog, which they said would take about three days.

"We are doing this as quickly as possible as the ash could come back any time," airport official Yulfiadi, who like many Indonesians goes by one name, told AFP.

Between Thursday and Sunday, a total of 873 flights were cancelled or delayed, Yulfiadi said.

Most airlines resumed flights Sunday evening after the airport reopened, but Australian carriers Virgin Australia and Jetstar decided to keep services to and from Bali on hold. Many Australians are stuck in Bali after spending the school break on the island.

Virgin Australia also cancelled its flights to and from Bali Monday, saying their forecasters had warned that conditions were not suitable, while Jetstar resumed services during daylight hours.

Airport manager Trikora Harjo said the airport was operating normally again, adding: "The weather is good so I am not sure why one or two airlines have chosen not to fly."

- Holiday travel chaos -

The disruption also came at a bad time for Indonesians, as millions set off on holiday ahead of the Muslim celebration of Eid this week. The airport is providing buses for Indonesians seeking to leave Bali for the holy festival.

Authorities raised the alert status of Mount Raung late last month to the second highest level, after it began to spew lava and ash high into the air.

Indonesian government vulcanologist Gede Suantika said the wind was not blowing ash towards Bali Monday and he expected conditions to remain the same until at least the evening.

Besides Bali, two airports on Lombok island, also a popular holiday destination, and two small airports on Java serving domestic routes were closed by the ash cloud Thursday. All were now open except for one on Java.

Air traffic is regularly disrupted by volcanic eruptions in Indonesia, which sits on a belt of seismic activity running around the basin of the Pacific Ocean and is home to the highest number of active volcanoes in the world, around 130.

The main concern for airlines regarding volcanic ash is not that it can affect visibility but rather that it could damage jet engines, according to experts.

Ash turns into molten glass when it is sucked into aircraft engines and in extreme cases can cause them to shut down.

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Virgin Australia