The alert for a volcano belching huge plumes of smoke on Indonesia’s resort island of Bali has been raised to the highest level, officials said Monday, with fears a significant eruption could be imminent. The exclusion zone around Mount Agung, which is 75 kilometres (47 miles) from the tourist hub of Kuta, has been widened to 10 kilometers, with people living in the exclusion zone being urged to evacuate. “The volcano’s alert level has been raised to the highest level,” said senior state volcanologist Gede Suantika. “Constant tremors can be felt.” Huge plumes of smoke have been pouring out of the volcano since Tuesday and Suantika said it was belching thick grey smoke as high as 3,400 metres (11,154 feet) early Monday. About 25,000 people living nearby the mountain have already left their homes and evacuated since Mount Agung first started to spew smoke Tuesday. “Continuous ash puffs are sometimes accompanied by explosive eruptions accompanied by a weak sound of boom,” the National Board for Disaster Management wrote on Facebook. “The rays of fire are increasingly observed at night. This indicates the potential for a larger eruption is imminent.” National disaster agency spokesman Sutopo Purwo Nugroho called for people to stay calm. The airport in Bali’s capital Denpasar, a top holiday destination that attracts millions of foreign tourists every year, has been closed. “Bali’s airport has indeed been closed. We’re still coordinating the next steps,” airport spokesman Arie Ahsanurrohim told AFP. The Australian government put out a travel advisory Sunday instructing travellers to exercise a high degree of caution in Indonesia and follow the instructions of authorities. Mount Agung last erupted in 1963, killing about 1,600 people. It rumbled back to life in September and authorities raised the alert to the highest level, forcing 140,000 people living nearby to evacuate. The volcano’s activity decreased in late October and many people returned to their home as the alert was lowered to the second-highest level. But Mount Agung started rumbling again last Tuesday. Mount Agung is one of more than 120 active volcanoes extending the length of Indonesia, which straddles the Pacific Ring of Fire.