Fears of an imminent major eruption of Bali's Mount Agung have increased and the evacuation zone around the volcano has been widened.
Indonesian authorities have raised the state of alert to its highest level.
The island's airport has now closed, leaving thousands stranded in the tourist hotspot.
Authorities say dark smoke and ash have been billowing up to 3,400m (11,150ft) above the mountain's summit, which has also been emitting fire.
Officials have warned residents to stay away from rock and debris flows known as lahars, which have been spotted flowing down from the mountain.
The National Board for Disaster Management raised the alert to level four from 06:00 local time (22:00 GMT Sunday), because of "the possibility and imminent risk of disaster".
The volcano was seen emitting "continuous ash puffs" occasionally accompanied by "explosive eruptions" and "weak booms" 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 on its Facebook page.
The ash prompted officials to shut down Bali's Ngurah Rai airport from Monday to Tuesday morning. All flights during this period have been cancelled.
The Australian government and the UK's Foreign Office have advised travellers to be prepared for cancelled flights, closely monitor local media, and to heed local authorities' warnings.
China (statement in Chinese) advised its citizens to be "cautious" if travelling to Bali, while warning against non-essential travel to the affected region of the island.
The airport on neighbouring island Lombok reopened on Monday morning after it was shut briefly.
Officials have also been distributing masks for local residents, as ash rains down in the vicinity.
Anna Baranova, who works with non-governmental organisation Kopernik that is helping evacuees, said her group was trying to bring in better masks and possibly goggles.
Lahars, also known as "cold lava", are slurries of rock fragments mixed with water, and have been spotted in fields and rivers near the volcano.
The spokesman for the national disaster management agency, Sutopo Purwo Nugroho, has warned that lahars may increase due to heavy rain and as Mount Agung continues to emit pyroclastic material.
He has urged islanders to stay away from lahars as well as avoid activities near rivers.
Authorities first issued warnings of an imminent eruption and raised the alert to the highest level in September after detecting heightened volcanic activity, prompting mass evacuations.
But some islanders returned to their homes in October after the alert level was lowered with a decrease in activity.