A volcanic eruption in Bali could cause the Earth's temperature to drop.

More than 75,000 people have been evacuated from villages surrounding Mount Agung, about 75 kilometres from the popular tourist destination of Kuta, with the volcano threatening to erupt.

Hot magma has been seen pulsing only metres from the top of the volcano's mouth. An explosion could see lava reaching temperatures of up to 800C consume forests, crops, livestock and homes within a 10km radius.

And while the immediate flow of lava and ash would almost certainly cause a localised disaster, sulphur-rich volcanic gas being pumped into the atmosphere could wreak havoc in other ways.

Mount Agung volcano. (AP)

University of Queensland volcanology expert Dr Teresa Ubide told nine.com.au an eruption would likely see global temperatures drop, which could impact food sources.

The last time Agung erupted in 1963 killing more than 1,000 people, the massive amounts of sulphur being emitted into the air decreased the globe's temperature by 0.1 - 0.4 degrees Celsius.

"Mount Pinatubo in the Philippines decreased global temperatures by half a degree Celcius for the following two years after it erupted," she told nine.com.au.

"That half a degree can affect absolutely everything."

In 1815 the world faced a global temperature drop of about three degrees following another Indonesian eruption.

The volcano had been dormant for 120 years before 196 eruption. (AAP) (AAP)

Villages almost completely reduced to ash after 1963 eruption of Agung volcano in 1963. (AAP) (AAP)

A level seven eruption at Mount Tambora sent millions of tonnes of dust, ash and sulphur into the atmosphere, forming a haze that reduced the level of ultraviolet rays reaching the Earth's surface.

The devastating impact was felt in the following year, dubbed 'The Year without Summer', as people faced an outbreak of disease and near-famine conditions.

Crops failed and animals died across parts of North America and Europe, sparking food riots and widespread migration.

The last time Mount Agung erupted it sent a 10km high column of "toxic gas and hot ash" into the air as "destructive currents" poured down the mountain.

The area has seen more than 1,000 volcanic earthquakes over the last few days, with Dr Ubide warning they are increasing.

Lava flows down Mount Agung following eruption in 1963. (AAP) (AAP)

"It is becoming more frequent and shallow which suggests magma is rising to the surface and likely to erupt."

Dr Ubide said the volcano is located in the infamous Ring of Fire and considered quite large – with layers of hardened lava, pumice and volcanic ash forming its three-kilometre high peak.

She said it was "very common" to have strong eruptions in this area and warned Mount Agung had a history of powerful eruptions.

"If you open a bottle of champagne very gently it is most dangerous if you are up close. But if you shake the bottle, like an explosive eruption, you build up pressure and it will generate much bigger problems," she said.

"The previous eruptions we have known here have been large - and explosive - so we will likely see the same thing again."

Destruction of neighbouring villages after 1963 eruption of Agung volcano in Bali. (AAP) (AAP)

She said Indonesian authorities were well prepared for an eruption but cautioned that a pyroclastic flow, or fast moving currents made of volcanic matter and gasses that can exceed 1000C, would be more likely to cause widespread destruction if it rained after the eruption.

"They can come down the mountain really fast … the toxic gases and ash destroys everything. You don't want to be anywhere near that."

Dr Ubide said the recent increased seismic activity in the Ring of Fire – including earthquakes off the coast of Fiji and a volcanic eruption in Vanuatu – is being caused by the same geological process but aren't linked.