The volcano is producing giant plumes of volcanic ash and dangerous lahars after erupting at about 5.30pm local time on Saturday.
Tens of thousands of Balinese locals have been forced to abandon their homes and villages to escape the looming threat of a more violent eruption.
Mount Agung’s volcano alert was raised to the maximum level 4 overnight and its exclusion zone was extended to 8-10 kilometres this morning.
Indonesia’s Volcanology and Geological Disaster Mitigation Centre (PVMBG) said: “Grey ash and occasional weak blasts can be heard 12 km (seven miles) from the peak.
“Flames were visible at night which indicates a potential eruption could happen anytime.
“In anticipation of the possibility and imminent risk of disaster, the PVMBG raised Mount Agung’s alert level from three to four starting from 6am (local time).”
About 40,000 people had already been evacuated from the Bali volcano’s danger zone, but tens of thousands still need to move after the alert level was pushed up.
Officials hope to evacuate around 100,000 people in total.
How dangerous is the Bali volcano?
Due to its unpredictability, Mount Agung has the potential to be extremely deadly.
Professor Joachim Gottsmann, head of volcanology at Bristol University, has warned that it is extremely difficult to forecast volcanic eruptions.
Agung has already started producing dangerous mudflows known as lahars, sparking fears that the next eruption could cause pyroclastic flows.
Read more: WHAT IS A LAHAR?
Prof Gottsmann told Express.co.uk: “The eruption could end abruptly, continue as is or escalate to a major eruption.
“Pyroclastic flows are inevitable in case of the latter but also possible if the eruption continues as is,” Prof Gottsmann said.
“There are reports of a lava dome in the cater indicating that magma has now breached the surface.
“Domes are inherently unstable and one important source of pyroclastic flows.”
Mount Agung killed more than 1,100 people when it last erupted in 1953, with most of the deaths caused by pyroclastic flows.
Officials are confident that the swift evacuation process this time round will help keep the death toll far below the last eruption.
Professor Mike Burton, who chairs the Volcanology department at the University of Manchester, believes modern monitoring techniques make this goal possible.
He said: “There is much better awareness of the hazards posed by explosive eruptions and, most importantly, local populations are better informed, with clearer communication links.
“Therefore, planning for a scenario similar to the 1963 eruption with pyroclastic flow run out up to 12 km from the summit is prudent, with a good probability that the actual eruption will be smaller than that.”
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