Indonesia situated Mount Agung's volcanic tremors first began in September.
Since last week dark gas and ash have been billowing up to 3,400m (11,150ft) above the mountain's summit. The volcano is emitting "continuous ash puffs" with occasional "explosive eruptions" that could be heard 12km (7 miles) from the summit. "The rays of fire are increasingly observed at night. This indicates the potential for a larger eruption is imminent," it said in a statement (in Indonesian) on its Facebook page.
Tens of thousands of people stayed put near Mount Agung after an alert was raised to its highest level. Some still felt safe while others did not want to leave livestock.
A spokesman for the Indonesia's National Disaster Management Agency (BNPB) said people were checking the exclusion zone for non-evacuees.
"There are personnel doing the sweeping, if they [residents] need to be forcibly evacuated," Sutopo Purwo Nugroho said.
The closure of the island's airport was extended for a second day, leaving thousands stranded in the tourist hotspot.
Up to 100,000 people live in the area that could potentially be affected by streams of burning rock have been spotted flowing down from the mountain. But by Monday only 40,000 had left.
The BNPB raised the alert to level four from 06:00 local time (22:00 GMT on Sunday) because of an "imminent risk of disaster".
According to official estimates, the holiday island lost at least $110m in tourism and productivity during that major evacuation.
The main tourist stretch of Kuta and Seminyak is about 70km (43 miles) from the volcano, far beyond the exclusion zone.
But the ash prompted officials to shut down Bali's Ngurah Rai airport from Monday to Tuesday morning.
Airport authorities said 445 flights had been cancelled, affecting 59,000 travellers, while Indonesia's hotel association said stranded tourists staying at member hotels could stay one night for free.
The Australian government issued travel advice saying : "Volcanic activity may escalate with little or no notice".
The UK's Foreign Office have advised travellers to be prepared for cancelled flights, closely monitor local media, and to heed local authorities' warnings.