Mount Agung volcano on Bali has erupted for the first time in more than half a century, forcing closure of the Indonesian tourist island's busy airport as the mountain gushes huge columns of ash that are a threat to airplanes.

Indonesia's National Disaster Mitigation Agency raised the volcano's alert to the highest level and expanded an exclusion zone to 10 kilometers (6 miles) from the crater. It said a larger eruption is possible, though a government volcanologist has also said Agung could stay at its current level of activity for weeks and not erupt explosively.

Authorities have told 100,000 people to leave homes nearest the volcano, though tens of thousands stayed because they felt safe or didn't want to abandon livestock.

Agung'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.

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

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