Bali's Ngurah Rai airport will remain closed until at least Wednesday morning local time.
"The Volcanic Ash Advisory shows that the plane routes have been covered by volcanic ash, this is dangerous for the flights," Indonesian AirNav official Wisnu Darjono said.
Indonesia has warned the first major eruption of Mt Agung on the tourist island of Bali is imminent, with authorities closing the airport and ordering 100,000 residents living near the volcano to evacuate the area immediately.
But thousands haven't left despite authorities raising the alert to its highest level, and forcible evictions may be enforced, a spokesman for the country's National Disaster Management Agency (BNPB) said.
"There are personnel doing the sweeping, if they [residents] need to be forcibly evacuated," Sutopo Purwo Nugroho said.
The airport was originally closed for 24 hours from Monday morning, disrupting 445 flights and stranding about 59,000 passengers, after Mount Agung sent volcanic ash high into the sky. Officials said cancellations could be extended.
An empty Bali International Airport is seen after volcanic ash forced its closure on Monday, November 27, 2017 (AAP) Source: AAP
"Plumes of smoke are occasionally accompanied by explosive eruptions and the sound of weak blasts that can be heard up to 12km from the peak," the Disaster Mitigation Agency said in a statement after raising the alert from three to its highest level of four.
"The potential for a larger eruption is imminent," it said, referring to a visible glow of magma at Mount Agung's peak overnight and warning residents to evacuate a danger zone at a radius of 8-10km.
Video footage shared by the agency showed volcanic mud flows (lahar) on the mountainside. Lahar carrying mud and large boulders can destroy houses, bridges and roads in its path.
Bali airport, about 60km from the volcano, will be closed for 24 hours, its operator said.
Ten alternative airports have been prepared for airlines to divert inbound flights, including in neighbouring provinces.
Virgin Australia said it was cancelling flights on Tuesday, while Jetstar was offering to exchange Bali bound tickets for other destinations.
Television footage showed hundreds of holidaymakers camped inside the airport terminal, some sleeping on their bags, others using mobile telephones.
Some travellers had retired for the night on makeshift beds on the terminal's dusty floors. Others were considering a more than 10-hour journey across land to the city of Surabaya to begin a string of flights across Indonesia and eventually to Australia.
But all were frustrated by the lack of information from the airlines.
People gather on the banks of the Yeh Sah River in Karangasem Regency of Bali, Indonesia on November 27, 2017 to observe the lahar from Mount Agung (AAP) Source: AAP
The first Janeen McKay heard of the cancellations was a text from her brother back in Australia just before she arrived at the airport.
"I had nothing from Jetstar, they had my mobile number," she told AAP.
She had been waiting for nearly 12 hours and was told by the airline she couldn't get home until Saturday.
Ms McKay, an office manager, said she needed to get back to Geraldton to take care of her elderly mother, while her sister, Wendy Lynch, needed to be at work as a nurse on Thursday.
"We had a really nice time in Bali but then we get here and this has just ruined it," Ms McKay said.
"Why does it take five days to get us out of here?
"Not very happy."
Veronika Naberezhnova said she was resigned to the waiting game too.
"It's a bit annoying," the Department of Human Services employee said.
"My family's waiting there (in Sydney) as well, they're all waiting, they're all stressed."
Cover-More, Australia's biggest travel insurer, said on its website customers would only be covered if they had bought policies before the volcano alert was first issued on September 18.
Indonesia's hotel and restaurant association said stranded tourists at member hotels would get one night's free stay.
Mt Agung sits more than 3000 metres high over eastern Bali.
Australia's Bureau of Meteorology's Volanic Ash Advisory Centre in Darwin issued maps showing an ash cloud heading southeast over the neighbouring island of Lombok away from Bali's capital Denpasar, where the international airport is located.
Thick clouds of smokes are seen from the Mount Agung volcano during an eruption in the district of Karangasem, Bali (AAP) Source: AAP
The ring of fire
Mount Agung last erupted in 1963, killing nearly 1,600 people.
It rumbled back to life in September and authorities raised the alert to the highest level, forcing 140,000 people living nearby to evacuate.
The volcano's activity decreased in late October and many people returned to their home as the alert was lowered to the second-highest level.
But Mount Agung rumbled again last Tuesday, forcing at least 25,000 people to seek shelter. Authorities urged people living within 7.5 kilometres (4.5 miles) of the mountain to evacuate.
The mountain sent smoke up into the air on Saturday for the second time in a week in what volcanologists call a phreatic eruption – one which is caused by the heating and expansion of groundwater.
Dozens of Balinese Hindus took part in ceremonies near the volcano on Sunday, offering prayers in the hope of preventing an eruption.
Officials later on Sunday said the activity could be a magmatic eruption – one which involves the decompression of gas and results in the spewing of ash – and advised people near the mountain to wear masks.
But authorities have decided not to raise the alert back to the highest level just yet.
"This time the tremors and quakes caused by the volcano's activities are significantly less than in September," said the head of Indonesia's volcanology centre Kasbani.
In September hundreds of tremors happened daily near Mount Agung, while during the past few days only a couple of tremors could be felt.
Mount Agung is one of more than 120 active volcanoes extending the length of Indonesia, which straddles the Pacific Ring of Fire.
