Nearly 60,000 travellers were stranded in Bali after the island's main airport was closed yesterday due to the eruption of Mount Agung, and the Indonesian authorities raised the threat warning to the highest level after its eruptions intensified.
The disaster management agency (BNPB) said 100,000 people would have to leave the danger zone around the mountain, up from 40,000 evacuees now.
BNPB, at a press conference in Jakarta yesterday, warned of the growing risk from lava and mudflows, and urged all remaining villagers in the 8km to 10km danger zone to leave.
The 3,000m-tall volcano has been belching huge amounts of ash high into the air, forcing Bali's Ngurah Rai airport to close yesterday for 24 hours. The airport said in a statement that 445 flights - 196 international and 249 domestic - and 59,000 passengers were affected.
Bali Governor I Made Mangku Pastika said the closure of the Ngurah Rai International Airport could last longer than 24 hours.
"We don't know how long it will be closed for," he told reporters. "Sure, it's been closed for 24 hours until tomorrow, but that doesn't rule out the possibility the (closure) could be extended," Reuters quoted him as saying.
On the neighbouring island of Lombok, the international airport resumed some flights yesterday after it was closed on Sunday due to ash clouds, which are moving now in a more southerly direction. Abrasive ash clouds are a danger to aviation and can badly damage aircraft engines.
Mount Agung lies some 70km from Bali's main airport and its top tourist areas, which attract some five million tourists annually.
Mount Agung has been rumbling since September, forcing tens of thousands of people to flee to shelters. It began a series of mild eruptions, called phreatic eruptions, last week.
The nature of the eruptions has changed, the BNPB has said, with lava now spewing out. Lava is molten rock or magma.
On Sunday night, a bright orange glow at the volcano's summit could be seen, signalling that potentially greater eruptions are very imminent, the BNPB said.
The agency issued the level four warning alert, which is the highest possible, at 6am yesterday.
Tremors have also greatly increased.
"Eruptions, tremors are continuing until now. Lava is filling up the crater, and will spill over any time and flow down the slope," BNPB spokesman Sutopo Purwo Nugroho told reporters at the press conference yesterday.
But he also said the expected major eruption will not be as large as the one from 1963 to 1964, the last time the mountain exploded into life in a series of eruptions that killed more than 1,500 people.
"Agung's impending major eruption will not be as big as that in 1963, based on analysis of magma condition, how far ash travels above the crater," he said. "In 1963, ash spewed travelled 20km high, while this time round it is only 3.5km to 4km (above the crater)."
The volcano, which began to spew lava last Saturday, has continuously ejected ash while the booming sound of intermittent eruptions can be heard as far as 12km away.
Residents have been told to evacuate the danger zone, which has been expanded to between 8km and 10km, up from 6km to 7.5km.
Dr Sutopo warned of the risks of hot gases and lahar flows, pointing to the start of the wet season. Lahar flows (sometimes called cold lava) is a type of mudflow or debris flow composed of a slurry of volcanic material and water.
The authorities have been ordered to immediately distribute masks to several villages in affected areas.
Indonesia's hotel and restaurant association said yesterday that stranded tourists at member hotels would get one night's free stay.