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Airlines have issued a shock "red warning" about the impending danger of volcanic ash in the skies over Bali, following the second emission from Mount Agung this week. Emergency authorities have handed out eerie masks to local residents and tourists trapped on the island as fears grow about an imminent major eruption. On Sunday night Mount Agung emitted a thick plume of smoke reaching 4,000m (13,100 feet), which has thrown airports into disarray and tourists into a panic. The latest alert - a red warning - means an eruption is forecast to be "imminent" after nearby locals spotted volcanic ash rain.

GETTY Increased volcanic activity had prompted fears a major eruption was imminent

YOUTUBE Mount Agung emitted a thick plume of smoke reaching 4,000m

In shock live footage, the distant volcano can be seen emitting thick ash in the video below while brave monitors look on across the forest. Authorities have told people within a 7.5km exclusion zone to "immediately evacuate" in an "orderly and calm manner". Bali is a major tourist destination, and major airlines have already cancelled flights to and from the island amid fears of ash disrupting plane engines. On the island of Lombok, the main international airport has been closed entirely.

TWITTER Major airlines have already cancelled flights to and from the island

The latest alert - a red warning - means a major eruption is forecast to be imminent

About 25,000 people are thought to be in shelters while more than 140,000 people fled earlier this year. According to official estimates, the holiday island has already lost at least £83m in tourism and productivity due to the major evacuation. Indonesia sits on the Pacific Ring of Fire where tectonic plates collide, causing frequent seismic and volcanic activity. The last time Mount Agung erupted, in 1963, more than 1,000 people died. Australia's Bureau of Meteorology said in an advisory from it's Volcanic Ash Advisory Centre (VACC) in Darwin the eruption was “expected to be ongoing”.

Gede Suantika, an official at the volcanology and geological disaster mitigation agency, said: "The activity of Mount Agung has entered the magmatic eruption phase, it is still spewing ash at the moment, but we need to monitor and be cautious over the possibility of a strong, explosive eruption.” Professor David Rothery, a volcanologist at the Open University, has warned that gas trapped within Mount Agung could cause a huge explosion and pyroclastic flows if it cannot escape. Speaking to Sky News, he said: “It’s a matter of whether that gas can escape passively, just by bubbling through the magma and cracks in the volcano, or whether it builds up to such a volume of gas that it blows out explosively and drives a very high column of fragmented ash into the sky. “A big heavy column being driven upwards can then collapse down and produce these horrible pyroclastic flows which sweep across the terrain.”

Sutopo Yuwono, from the National Disaster Mitigation Agency, warned that the island should brace for another eruption as “explosions” have already begun. He said: “The possibility of a large eruption is very high. Some indications show that there will indeed be an eruption. “Since yesterday the eruption that happened has been accompanied by a sound of explosions and vibrations that can be heard and felt within a distance of 12km.” Volcanologist Jacqueline Salzer warned that the erupting Mount Agung could be very deadly if it releases pyroclastic flows. Speaking to DW, she said: “If the magma's highly viscous, the volcano can be particularly explosive. “The reason is that gases are caught inside the magma, under pressure. She added: “It's an unbelievably fast event: The pyroclastic streams reach speeds of several hundred kilometres per hour. “Nobody can escape them. You have to be far enough away from the volcano – and early enough – to be safe.”