Jetstar has cancelled flights in and out of Bali as an ash cloud from a volcanic eruption in Indonesia drifts towards Denpasar International Airport.
Return flights to and from Cairns, Perth, Melbourne and Sydney, and one way flights to and from Singapore, Adelaide and Darwin are affected.
In a statement on its website, the airline said passengers on rescheduled or cancelled flights would be notified by Jetstar or their travel agent directly and provided with options to fly on alternative services.
Overnight, two Jetstar flights were turned back three hours into their journey.
The airline is planning to issue an update once it is daylight in Indonesia.
The ABC reported that Qantas staff in Darwin are preparing to announce delays.