Flights to and from Bali are expected to be canceled for at least the next 24 hours as the eruption of Mount Agung continues.
The Volcano Observatory Notice for Aviation (VONA) said a continuous emission had been observed at the volcano and was reaching a height of more than 23,000ft.
The ash cloud is moving to the west south-west and there was increasing seismic activity, it said.
VONA put the color code at orange — one below the top red level — meaning the volcano is exhibiting heightened unrest with an increased likelihood of eruption or an eruption is underway with no or minor ash emission.
The timing is unfortunate as it comes some Australian states enter the busy school holiday travel period.
AirAsia, Jetstar, and Virgin Australia confirmed they had canceled flights last night after ash from the volcano was blown close to Denpasar airport.
AirAsia canceled flights from Kuala Lumpur, Singapore, Perth, Jakarta, Surabaya and Manilla and postponed several others until further notice.
The airline said affected guests would be notified of their status via email and SMS and it was offering a number of recovery options, including full refunds.
They also included the ability to change a flight to a new travel date on the same route within 14 calendar days without additional costs (subject to seat availability) or retain the value of the fare for 90 days from the day of issue.
VAAC Mount Agung Volcanic Ash Graphic
Passengers were advised to check airasia.com and the airline’s social media channels for further details.
A Virgin spokeswoman said the airline had canceled a return flight to the holiday island and was expecting delays Friday.
She said the airline would reassess the situation today but cancellations are alsmot certain.
WATCH Virgin Australia's volcanic ash assessment video.
Jetstar said it had canceled six flights to Bali on Thursday from Sydney, Perth, Cairns, Melbourne and Adelaide. Four return flights to Adelaide, Perth Sydney and Melbourne were also axed.
Two flights on their way to Denpasar also returned to Australia and the Friday morning Denpasar-Cairns and Singapore-Denpasar-Perth flights were also canceled.
Qantas said a flight each from Sydney and Melbourne to Bali had turned back to Australia and two flights due to leave Bali Thursday night had been delayed.
A spokeswoman said customers on the delayed flights were being given accommodation and the airline was watching developments.
“We are monitoring the advice from the Volcanic Ash Advisory Centre and our team of senior pilots and meteorologists will make an assessment when flights can be resumed,'' she said.
"We will continue to provide customers with updates as the situation develops and contact them via email or SMS if their flight is affected.
"While these disruptions are frustrating, we always put safety first."
Qantas customers were advised to check their flight status on Qantas.com.
Mt Agung caused widespread disruptions towards the end of 2017, throwing the travel plans of thousands of holidaymakers into chaos.
More than 38,000 local residents have been evacuated to shelters and a 12km exclusive zone placed around the volcano, which is 70km from Kuta.
An eruption in 1963 killed almost 2000 people and was of the explosive intensity as Mount St Helens in 1981 and Mount Pinatubo in 1991.
