MORE than 100,000 people were ordered to leave a new and larger exclusion zone around the erupting Balinese volcano Mount Agung yesterday.

The island’s international airport was forced to close as ash from the volcano was spewed up to about 3000 metres (9800ft). Scientists predict that mud flows and molten lava flows will follow.

Video released by Indonesia’s National Board for Disaster Management showed an avalanche of volcanic debris and water known as a lahar moving down the side of the mountain. The board raised the volcano’s alert to the highest level early yesterday and expanded the danger zone to 10km (six miles) in places from the previous 7.5km. It said in a statement that a larger eruption is possible.

The alert was raised to level four late on Sunday due to “the possibility and imminent risk of disaster”. Some experts suggest the volcano may explode outwards as well as upwards.

Mount Agung was seen emitting continuous ash puffs, occasionally accompanied by explosive eruptions and booms that could be heard 12km (seven miles) away from the summit. “The rays of fire are increasingly observed at night. This indicates the potential for a larger eruption is imminent,” said disaster board spokesman Sutopo Purwo Nugroho.

He told a news conference in Jakarta that the extension of the danger zone affects 22 villages and about 90,000 to 100,000 people. He said about 40,000 people had already been evacuated but others have not left because they feel safe or don’t want to abandon their livestock. “Authorities will comb the area to persuade them,” he said. “If needed, we will forcibly evacuate them.”

About 25,000 people were already living in evacuation centres after an increase in tremors from the mountain in September. Bali’s airport, near the capital Denpasar, was closed early yesterday after ash reached its airspace. Almost 60,000 travellers were stranded by the cancellation of 445 flights, a spokesman said.

Information boards showed rows of grounded flights as tourists arrived at the busy airport expecting to catch flights home. The closure was due to be in effect until this morning.

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. Indonesia’s national hotel association said that stranded tourists staying at member hotels could stay one night for free. Australian and British foreign office staff have advised travellers to be prepared for cancelled flights. They are also being advised to closely monitor local media, and to heed local authorities’ warnings. China advised its citizens to be “cautious” if travelling to Bali.

Bali’s governor, Made Pastika, said he was urging hotels on the island to allow stranded foreign tourists to stay free of charge, especially cash-strapped backpackers. “Yes, I’m asking. This is a disaster. Especially for those who have spent all their money,” he said. Pastika was coordinating with the immigration office to ensure the extension of visas for tourists forced to overstay due to the volcanic activity.

Brandon Olsen, a Canadian stranded at the airport, said: “We now have to find a hotel and spend more of our money that they’re not going to cover us for when we get home, unfortunately.”

Putu Sulasmi had evacuated with her husband and other family members to a sports centre.

She said: “We came here on motorcycles. We had to evacuate because our house is just three miles from the mountain. We were so scared with the thundering sound and red light.”

The family had stayed at the same sports centre in September and October when the volcano’s alert was at the highest level for several weeks but it did not erupt. They returned to their village about a week ago. “If it has to erupt, let it erupt now rather than leaving us in uncertainty. I’ll just accept it if our house is destroyed,” Sulasmi said.

Geologist Mark Tingay of the University of Adelaide said Mount Agung appears to be entering the next phase with a magmatic eruption, where the glow of lava is visible from the crater.

But he added that it was “very hard to tell” how the situation would develop. “These eruptions can be quite large and extensive and violent, but this could also be a relatively minor eruption over time.”

He added that Indonesian authorities had made preparations for an eruption for months, and said they appeared “extremely well prepared”, with the situation “well under control”.