Indonesia has issued its highest-level aviation warning for flights around Bali as a shifting cloud of volcanic ash closed the airport on the holiday island of Lombok and forced the cancellation of flights for thousands of passengers.
Air Asia was the latest airline to cancel flights, following earlier moves by Jetstar and Qantas.
Staff at Indonesia's volcano monitoring centre said it was not just pulverised rock being blown out of Mt Agung, but magma has now reached the volcano's surface.
So far there have been no new evacuations or extension of the island's no-go zone.
The flights of about 5,000 passengers were cancelled on Sunday and another 2,500 holidaymakers could not get in because their planes were rerouted or never took off.
The same could happen on Monday.
It is likely the volcano will continue erupting.
Indonesia's disaster management agency said the eruptions were no longer "phreatic", which means they are triggered by water hitting superheated rocks and usually short-lived.
They were now magmatic eruptions, the agency said, which means lava has forced its way to the surface.
A plume of pulverised rock is blowing south-east from Mt Agung, forcing the closure of Lombok's airport until at least 6:00am (local time) on Monday.
Airport preparing for worst-case scenario
It is also affecting some flight paths to Denpasar and creating complications for air traffic controllers who are steering planes away from the ash.
The aviation alert status for Bali has been lifted from "orange" to "red" but the airport will remain open until volcanic dust impacts the airport.
"Once the airports find volcanic ash trace, we'll close down the airport for flights," said Herson, chief of Bali's Ngurah Rai airport.
The airport authority is preparing for the worst-case scenario — a total closure caused by a shifting ash cloud, Herson said.
If that happens, 50,000 passengers a day will be stuck in Bali.
"What has been also prepared are the closest airports, where aircraft en route which could not reach Ngurah Rai have landed at," Herson said.
"The six closest airports including Surabaya, Makassar and some others which will be ready to back up Ngurah Rai, in case an immediate closing occurs."
Away from the airport, closer to the volcano, there are no new evacuations and so far no plans to extend an evacuation zone that reaches up to 7.5 kilometres from the crater.
About 30,000 Balinese people are still living in temporary shelters.
They will not be able to go home until the volcano's eruptions stop.
