A grey plume began coming out from Mt Agung in the afternoon. Both Jetstar Airways and Virgin Australia also said Tuesday night that their flights to and from Bali were operating as scheduled. People are being warned to stay away from the 6 to 7.5 kilometre volcano exclusion zone specified by the Centre for Volcanology on October 29. The National Disaster Management Agency described the eruption as "phreatic", which is a steam-driven explosion that occurs when water beneath the ground or on the surface is heated by molten rock, known as magma, lava, hot rocks or new volcanic deposits. "Phreatic eruption is difficult to predict. It can happen suddenly and there is often no sign of increased seismicity," said spokesman Sutopo Purwo Nugroho.

The alert level remains at three after being downgraded from the maximum level of four on October 29. He stressed there had been no upgrade to the alert status of the volcano. "People are encouraged to remain calm. Do not panic and believe misleading issues. Ngurah Rai International Airport is still safe and normal. Tourism in Bali is also safe, other than the dangerous radius around Mount Agung." He said the Centre for Volcanology would continue to monitor and analyse volcanic activity and provide up-to-date information. "Continuous tremors begin to be detected."

Mr Sutopo said phreatic eruptions were not too dangerous compared to magmatic eruptions, which involve the decompression of gas within molten rock. "Usually the impact of the (phreatic) eruption is ash rain, sand or gravel around the mountain," he said. Mr Sutopo said phreatic eruptions could occur without magmatic eruptions or could be the precursor for magmatic eruptions, as was the case with Mount Sinabung in Sumatra. Volcanoes in Indonesia had also had phreatic eruptions when they were only at alert level two, such as Mount Dempo, Mount Dieng, Mount Gamalama, Mount Merapi and others. "People's understanding of volcanoes is still quite limited. We have 127 volcanoes in Indonesia, each of which has different temperaments."

Ngurah Rai International Airport spokesman Arie Ahsan said visual observation via pilot reports was ongoing. "The wind is blowing to the east with tendency towards southeast," he said. Virgin Australia said it was closely monitoring activity at Mt Agung in Bali. It said the current aviation colour code from the Agung Volcano Observatory has recently been updated to orange. "We encourage guests booked via travel agents or third parties to ensure Virgin Australia has your mobile number, should we need to contact you in the event of any changes," Virgin Australia said in a statement.

Guests with travel insurance were also encouraged to check with their insurer about their individual circumstances. "At this point this is very, very small," tweeted New Zealand volcanologist Dr Janine Krippner. "Right now this is not a serious eruption but of course this can change. Time to make sure you are prepared and keep an eye on official Agung information." An Indonesian government press release said a potential danger was heavy ash rain that could spread outside of the danger zone.

"It is expected that all communities living around Mount Agung and on the island of Bali, immediately prepare a mask to cover the nose and mouth and eye protection as an effort to anticipate the potential danger volcanic ash," it said in a statement. Refugee Kadek Nadi, who lives in the exclusion zone about four kilometres from the summit, was told by Fairfax Media the volcano was erupting. He said he was currently at home in Pasar Agung but his family were at the refugee camp. "Dark smoke is now coming from the summit," he said. "I am heading down (the mountain) now." In late October there were 134,500 evacuees living in 390 refugee camps in nine regencies throughout Bali.

However after the threat alert was downgraded all but 29,000 have returned to their homes. Follow Jewel Topsfield on Facebook