Australia has issued a new travel advisory for Bali as experts warn the island's enormous volcano, Mt Agung, could erupt soon.
Hundreds of tremors each day are shaking the volcano, and the region's leading vulcanologist has said the probability of an eruption is increasing by the day.
Dr Devy Kamil Syahbana has said tourists should be ready to change their plans if the volcano erupts.
The most likely initial impact of a big eruption is the closure of the island's airport.
The Department of Foreign Affairs and Trade said tourists to Bali should reconfirm their trips with their airlines and tour operators.
Hundreds of locals have been moved from their villages on the lower slopes of the volcano.
Mt Agung has not erupted yet and flights to Bali are not affected but an exclusion zone around the volcano is already affecting tours and trekking groups.
Seismic monitoring equipment on the volcano recorded 676 tremors on Thursday caused by lava pushing through layers of rock deep beneath the mountain, and in one six-hour period on Friday morning there were another 178 tremors.
Dr Syahbana, the head of volcano mitigation for eastern Indonesia, said the tremors were coming from inside the volcano.
"Our data shows the number of earthquakes is still increasing, which shows that the magma has very huge energy," he said.
"It means we have to be alert to the situation but we don't need to panic."
He said the earthquakes themselves were evidence of the potential eruption.
"Magma is pushing to all directions, finding the softest path," he said.
"At the moment when the magma succeeds to go in a certain path, it creates an earthquake — it opens the path to go to the surface.
Dr Syahbana is monitoring Mt Agung from an observation station about 12km from the volcano's crater.
He said it was impossible to predict the size of the Agung eruption, if it erupted.
The volcano has not erupted since 1963, when about 1,000 people died.
Dr Syahbana said that eruption was a 5 on the Volcano Explosivity Index (VEI) — a massive eruption that is far bigger than any recent eruptions in Indonesia.
The explosions on Mt Sinabung earlier this year only rated a VEI of 2, Dr Syahbana said.
He said tourists could still come to Bali, but they must be ready if anything changed.
"If something is changing, you need to be prepared for that," he said.
"We're not even sure this volcano will erupt. It's possible for the magma to be exhausted and for this crisis to end. That's the possibility we're hoping for."