Indonesian authorities have doubled the exclusion zone around Bali's Mount Agung with fears the volcano could erupt in the coming days or weeks.
The 7.5 kilometre exclusion zone has been set up around the volcano's crater and a 14-day emergency alert period is in place.
The alert has raised concerns for people travelling to Bali for school holidays, which commence on Saturday.
On Wednesday morning, flights out of Perth Airport remained unaffected but travellers are being urged to check with their airlines before flying.
The volcano is around 70 kilometres from the popular tourist destination of Kuta.
National Disaster Management Agency spokesman Sutopo Nugroho said on Tuesday harmonic tremors continued to increase around the volcano.
It last erupted in 1963, killing more than 1000 people.
Aviation expert Ellis Taylor told Nine News Perth airlines could make the decision to cancel flights just hours in advance, depending on weather conditions.
"Volcanoic ash is a really big problem for airlines because if that ash gets into engines, it can shut them down and there has been occurrences where aircraft have lost all their engines after flying through volcanic ash and that's why they take a really cautious approach," he said.
Indonesia sits on the Pacific Ring of Fire, an area known for frequent seismic upheavals and volcanic eruptions. The country is home to about 130 active volcanoes.
- with AAP
