Mount Agung erupted on Tuesday, three months after it first started rumbling. The volcano's status is set at the third highest alert level, the National Disaster Mitigation Agency (BNPB) has previously said.
The number of evacuees dropped to about 30,000 after the alert level was lowered.
Bali's Ngurah Rai International Airport remains open and flights are operating as scheduled, but that could change if ash enters the flight path. "It is the smoke", said to AFP Made Indra, a manager of the centre in Bali.
"A phreatic eruption is basically one where there is no magma involved". It can happen suddenly and there is often no sign of increased seismicity.
He stressed there had been no upgrade to the alert status of the volcano. Do not panic and believe misleading issues.
The island's aviation alert has been increased to orange as per procedure but the busy global airport remains open. Other areas in Bali are also safe.
"Smoke is observed with medium pressure with a thick grey colour and with a maximum height of about 1km above the peak", local authorities said. "Continuous tremors begin to be detected".
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Eruptions could result in ash clouds that could "severely disrupt air travel", it said.
"People's understanding of volcanoes is still quite limited". We've all seen the steaming, the steam plume at the top of the volcano.
US-based volcanologist Dr Janine Krippner has been following Mt Agung's rumblings since September.
It's unclear whether further eruptions will occur. "Time to make sure you are prepared and keep an eye on official Agung information".
There is now an evacuation zone around the volcano, which stretches between six to 7.5km from the summit. "I am heading down (the mountain) now".
That alert was recently downgraded.