The Volcanology and Geological Disaster Mitigation Agency (PVMBG) said that greyish-white plumes have soared as high as 2,000m above the crater.
The 10-kilometre radius around Mount Agung is littered with roadside signs that read "Volcanic danger zone. No entry!", underscoring the potential risks.
The transport ministry has prepared 100 buses as well as ferries to carry stranded passengers to operating airports on Java and Lombok islands.