Indonesia's disaster mitigation agency said 40,000 people had been evacuated from near Bali's erupting Mount Agung volcano, but tens of thousands still needed to move with an imminent large eruption warning early on Monday.
"We really ask people in the danger zone to evacuate immediately because there's a potential for a bigger eruption," said Sutopo, a spokesman for Indonesia's disaster mitigation agency (BNPB).
He told a briefing that 40,000 people had evacuated out of around 90,000-100,000 residents estimated in the 8-10 km (5-6 miles) exclusion zone around Agung.
"Not all residents have evacuated yet. There are those (who haven't evacuated) because their farm animals haven't been evacuated yet. There are those who feel they are safe," he said, adding that security personnel were trying to persuade people to leave but they could be evacuated by force.
The volcano has been hurling clouds of white and dark grey ash about 3,000 metres (9,800 feet) into the atmosphere since the weekend.
Video released by the national disaster agency showed a mudflow of volcanic debris and water known as a lahar moving down the volcano's slopes.
Tests indicated ash had reached the island's airspace, leaving tourists facing flight information boards showing rows of cancellations as they arrived at the busy airport expecting to catch flights home.
Airport spokesman Air Ahsanurrohim said 445 flights were cancelled, affecting about 59,000 travellers. The closure is in effect until Tuesday morning, but officials said the situation would be reviewed every six hours.
Bali is Indonesia's top tourist destination, with its gentle Hindu culture, surf beaches and lush green interior attracting about five million visitors a year.
Geological agency head, Kasbani, who goes by one name, said the alert level was raised because the volcano had shifted from steam-based eruptions to magmatic eruptions.
"We don't expect a big eruption but we have to stay alert and anticipate," he said on Indonesian TV.
The exclusion zone around the crater was widened to six miles, from a previous three to five miles.
Ash up to half a centimetre (less than half an inch) thick settled on villages around the volcano over the weekend, and soldiers and police distributed masks.
The volcano's last major eruption in 1963 killed about 1,100 people.
Indonesia sits on the "Pacific Ring of Fire" and has more than 120 active volcanoes.
Mount Agung's alert status was raised to the highest level in September following a dramatic increase in tremors from the volcano, which doubled the exclusion zone around the crater and prompted more than 140,000 people to leave the area. The alert was lowered on October 29 after a decrease in activity, but about 25,000 people remained in evacuation centres.