Hundreds of flights from Australia to the Indonesian island of Bali were delayed or cancelled on Friday, when Mount Agung volcano erupted in the early hours of the morning, shooting ash 2,000 meters into the sky.

Bali is one of the top international holiday destinations for Australians and the closure of its main airport has left thousands of passengers not knowing when they will be able to depart.

"Based on the flight time out of Melbourne, it's possible some flights may still depart today, but we'll have to take our guidance from the airlines once they're notified what's happening on the ground there," spokesman for Australia's Melbourne Airport Grant Smith said.

The groundings come just one day before the school holiday period is set to commence in several Aussie States, and so far all major airlines including Qantas, AirAsia and Virgin have been affected.

"The plume itself is extending out to the west and south west, which has implications for Denpasar airport," acting manager of Australia's Bureau of Meteorology's Volcanic Ash Advisory Centre, Tristan King said.

"At the moment we have advised that there is ash over the airport, but if the winds do change direction they can take the ash away from busy areas of aviation."

King also said that southwesterly winds expected for Saturday morning may be favourable to clear some of the ash away from the airport.

Mount Agung has technically been erupting for months but in what experts call a "discreet" fashion, where small puffs of ash are emitted but dissipate quickly.

Denpasar airport was closed in November of 2017 and 150,000 local residents were evacuated when Agung erupted in a similar fashion.

Made up of fine pulverised rock, minerals and glass, volcanic ash in the air is accompanied by gases which convert into droplets of sulphuric acid and other substances.

This ash can be catastrophic for aircraft, potentially causing engines failure as well as abrasive damage to the fuselage and clogging fuel and cooling systems.