KARANGASEM: A rumbling volcano on the Indonesian resort island of Bali spewed smoke hundreds of metres into the air Saturday, officials said, just days after thousands were forced to flee over fears it would erupt.

Mount Agung belched smoke as high as 1,500 metres (4,900 feet) above its summit, twice as high as on Tuesday when smoke sparked an exodus from settlements near the mountain.

There are fears the volcano could erupt for the first time since 1963, when nearly 1,600 people died.

People living within 7.5 kilometres (4.5 miles) of the mountain have been told to evacuate, senior volcanologist Gede Suantika said, advising residents to remain calm.

It comes after the volcano stirred to life in September, forcing 140,000 people to leave the area.

Many returned home after the volcano´s activity waned, but fresh smoke has sparked a further exodus and around 25,000 people have been evacuated to more than 200 temporary shelters.

"We will continue to see eruptions like this on similar scales, but we cannot predict when Mount Agung will really erupt," Suantika told AFP.

The volcano´s alert level remains at the second-highest, he added.

Bali is a major tourist hub and its airport is operating normally, but some airlines have decided to cancel their flights.

Indonesia lies on the Pacific "Ring of Fire", where tectonic plates collide, causing frequent volcanic and seismic activity.

Mount Sinabung on Sumatra island -- which is currently at its highest alert level -- has been active since 2013.