Darwin remains cut off from all air services and flights from Australia to Bali are being affected as three separate ash plumes billow from an Indonesian volcano.
Mt Sangeang Api off the island of Sumbawa is erupting continuously after an initial blast on Friday afternoon, said meteorologist Tim Birch, from the Volcanic Ash Advisory Centre in Darwin.
Last night, he predicted: "We will see the plume here start to move east. It will start to move out of the Northern Territory and move steadily east in the location of Mt Isa [in Queensland] and it will start to dissipate."
But it would continue to affect Darwin flights today.
A second cloud, hovering north of Darwin between 9.5km and 16km in the air, might cause problems for flights between Australia and Malaysia and Singapore, he said.
A third, lower-level plume is drifting west from the volcano and is within 100km of Bali.
"The volcano is still erupting, as it has done for most of the day; not as violently as it initially erupted, but there is a steady plume," Birch said.
Fine particles of pulverised rock consisting mainly of silica contained in volcanic ash clouds can be highly abrasive and damage aircraft engines, structures and windows.
Virgin Australia cancelled all its flights yesterday to Darwin, spokeswoman Jacqui Abbott said.
"Our meteorologists are monitoring the situation and are consulting with the [volcanic ash] advisory centre in Darwin and we will renew normal operations as the situation allows."
Qantas spokeswoman Kira Reed said cancellations also affected all its Darwin flights yesterday and subsidiary Jetstar's services between the city and Cairns, Adelaide, Bali and Singapore.
The Volcanic Ash Advisory Centre manager, Emile Jansons, said last night that the ash cloud had also reached the Kimberley coast in Western Australia.
"It is spreading east and it may dissipate, so it is not clear how far east it will get. It is not yet clear if it will affect the eastern seaboard."
Jansons said the cloud was also spreading south, but the situation could change at any time.
"It is continuing to disperse but it is moving very rapidly - at 70 to 80 knots [130 to 150km/h] towards Alice Springs. There is a very strong jet stream so the boundary [of the cloud] may come further south."
Deputy Prime Minister Warren Truss said the ash cloud sat between 6km and 13km in the atmosphere and was sweeping southwest over northern Australia.
"Depending on wind and other weather conditions, the ash has the potential to affect flights to and from other airports, including Brisbane, during coming days. This is currently being fully assessed."
Volcanic activity on the mountain has been increasing over the past two weeks and locals have been warned to stay outside a 5km radius from the crater.
The mountain has been closed to climbers.
The volcano, which is 1981m above sea level, is on the 152sq km Sangiang Island. It last erupted in 1997 and 1999, and major activity in 1985 forced local farmers to flee.