KARANGASEM, Indonesia -- Indonesian authorities ordered a mass evacuation of people Monday from an expanded danger zone around an erupting volcano on Bali that has forced the island's international airport to close, stranding tens of thousands of travelers.

Mount Agung has been hurling clouds of white and dark gray ash about 9,800 feet into the atmosphere since the weekend. Video released by the National Disaster Mitigation Agency showed a mudflow of volcanic debris and water known as a lahar moving down the volcano's slopes.

The agency raised the volcano's alert to the highest level early Monday and expanded the danger zone to 6 miles in places from the previous 4.7 miles. It said in a statement that a larger eruption was possible.

A view of Mount Agung volcano erupting from Kubu, in Karangasem, Bali, Indonesia, Nov. 27, 2017. REUTERS

Spokesman Sutopo Purwo Nugroho 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 have evacuated but others have not left because they feel safe or don't want to abandon their livestock.

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"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 centers after an increase in tremors from the mountain in September sparked an evacuation.

Bali's airport was closed early Monday after ash reached its airspace.

Flight information boards showed rows of cancelations as tourists arrived at the busy airport expecting to catch flights home.

Airport spokesman Air Ahsanurrohim said 445 flights were canceled, stranding about 59,000 travelers. The closure is in effect until Tuesday morning though officials said the situation will be reviewed every six hours.

Passengers ask staff about their flights after Ngurah Rai airport closed their operation due to eruption of Mount Agung in Bali resort island, Nov. 27, 2017 in this photo taken by Antara Foto. REUTERS

Bali is Indonesia's top tourist destination, with its gentle Hindu culture, surf beaches and lush green interior attracting about 5 million visitors a year.

Some flights to and from Bali were canceled on Saturday and Sunday but most had continued to operate normally as the towering ash clouds were moving east toward the neighboring island of Lombok.

"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," said Canadian tourist Brandon Olsen who was stranded at Bali's airport with his girlfriend.

Indonesia's Directorate General of Land Transportation said 100 buses are being deployed to Bali's international airport and to ferry terminals to help travelers stranded by the eruption of Mount Agung.

The agency's chief, Budi, said major ferry crossing points have been advised to prepare for a surge in passengers and vehicles. Stranded tourists could leave Bali by taking a ferry to neighboring Java and then travel by land to the nearest airports.

Mount Agung volcano is seen spewing smoke and ash in Bali, Indonesia, on Nov. 26, 2017, in this picture obtained from social media. Reuters

Geological agency head, Kasbani, who goes by one name, said the alert level was raised because the volcano has shifted from steam-based eruptions to magmatic eruptions. He told Indonesian television on Monday morning that he did not expect a big eruption but added "we have to stay alert and anticipate."

The volcano's last major eruption in 1963 killed about 1,100 people.

Ash has settled on villages and resorts around the volcano and soldiers and police distributed masks on the weekend.

In Karangasem district that surrounds the volcano, tourists stopped to watch the towering plumes of ash as children made their made to school.

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 Oct. 29 after a decrease in activity but about 25,000 people remained in evacuation centers.