Mount Agung, about 75 kilometres (47 miles) from the Indonesian tourist hub of Kuta, has been rumbling since August, threatening to erupt for the first time since 1963.
"The chance that an eruption will happen is quite big. But it cannot be predicted when it will happen," Sutopo Purwo Nugroho, spokesman for the disaster mitigation agency, said.
The increased frequency of tremors shows the magma continuing to move towards the surface, with the mountain entering a "critical phase", the spokesman said.
The Indonesian Center for Volcanology and Geological Hazard Mitigation said there has been an increase in volcanic tremors, with a total of 564 recorded Monday.
Evacuees have packed into temporary shelters or moved in with relatives. Some 2,000 cows have also been evacuated from the flanks of the volcano.
Balinese residents, international NGOs and the government have begun organising aid.
Vehicles filled with noodles, mineral water and blankets have been sent to the evacuation centres, while residents around the island have been collecting donations for those affected.
Bali's "sister village" programme and tradition of communal assistance means evacuees have been able to stay in villages outside the danger zone.
Around 62,000 people lived in the danger zone prior to the evacuations, according to the disaster mitigation agency.
I Ketut Subandi, head of logistics at the village of Tana Ampo, said basic food items like rice, instant noodles, cooking oil and water were most needed.
"This morning we were worried because we had limited rice supply, but now we have received more rice stocks from donors," Subandi said.
Indonesia's national disaster agency has dispatched 640,000 face masks, 12,500 mattresses, 8,400 blankets, 50 tents, and has a budget of $75,000 for assistance.
The central government has set aside a relief fund of nearly $150 million in case of an eruption.
Officials announced the highest possible alert level on Friday due to the increasing volcanic activity, and told people to stay at least nine kilometres away from the crater.
"Our preparedness will be the key for the mitigations of volcanic risks," Devy Kamil, a senior official at Indonesia's Center for Volcanology and Geological Hazard Mitigation, told AFP.
Trekking tours on the mountain have been cancelled by operators but officials have otherwise been at pains to assure tourists the island is safe.
The airport in Bali's capital Denpasar, through which millions of foreign tourists pass every year, has not been affected, but several countries including Australia and Singapore have put out a travel advisory.
Mount Agung is one of more than 120 active volcanoes extending the length of Indonesia, which straddles the Pacific Ring of Fire.
It last erupted in 1963, killing nearly 1,600 people and sending ash as far as the capital Jakarta.
