Explosions from the mountain have been heard more than seven miles away and red-hot lava is welling up in the crater, sometimes seen in the reddish glow of the huge ash plumes.
Indonesian authorities have raised the volcano’s alert to the highest level and expanded the danger zone to six miles.
And experts warned that a larger eruption is possible – adding that lava rising in the crater “will certainly spill over to the slopes”.
Officials at the Disaster Mitigation Agency said in a statement on Monday that a volcanic eruption is “imminent” though the exact scale remains unclear.
The statement read: “Continuing plumes of smoke are occasionally accompanied by explosive eruptions and the sound of weak blasts that can be heard up to 12 km (seven miles) from the peak.
“Rays of fire are increasingly visible from night to the following day. This indicates the potential for a larger eruption is imminent.”
Cold lava flows, known as lahar, has already flooded the rivers and canals of nearby villages, with many locals ignoring warnings to steer clear.
Hundreds of flights have been cancelled and the local airport remains closed for a second day, leaving about 59,000 tourists stranded on the Island.
But officials said they are closely monitoring the situation and will determine every six hours whether the airport should remain closed.
Spokesman Sutopo Purwo Nugroho said the extension of the danger zone affects another 22 villages and about 90,000 to 100,000 people.
He added that about 40,000 people have evacuated but others have not left because they feel safe or don’t want to abandon their livestock.
“Authorities will comb the area to persuade them,” he said. “If needed we will forcibly evacuate them.”
Officials have ordered the evacuation of 100,000 people living near the deadly volcano, whose last major eruption in 1963 killed about 1,100 people.
Terrifying video footage shows a lahar scooping up huge amounts of debris as it ploughs down the side of the Bali volcano.
The latest map produced showed a 10km exclusion zone being put in place to protect residents from the dangerous lahars.
The lahars form in rivers and are comprised of rocks, vegetation and volcanic ash.
A powerful lahar has the potential to destroy any house, bridge or road in its path, creating a huge cause for concern in the region.