A rumbling volcano on the holiday island of Bali is spewing steam and sulphurous fumes with more intensity, heightening fears of an eruption as officials said the number of evacuees had topped 144,000.

Mount Agung, 75 kilometres (47 miles) from the resort hub of Kuta, has been shaking since August and threatening to erupt for the first time since 1963 -- a potential blow to the island's lucrative tourism industry.

The Indonesian Center for Volcanology and Geological Hazard Mitigation said Friday that remote satellite sensing had picked up new steam emissions and thermal areas within the crater.

White steam clouds -- which contain sulphurous fumes -- have been observed rising 50 to 200 metres above the summit, the centre said.

"At this moment, the probability of an eruption is higher than the probability of no eruption; however, the probability may change," said Kasbani, the centre's head volcanologist who like many Indonesians goes by one name.

Another of the volcanologists at the centre, Gede Suandika, said the more frequent emission of sulphurous fumes in the past three days indicated the volcano was changing.

"This morning the steam billowed from the crater like the smoke that comes out of a factory chimney," he said.

"Since the sulphurous fumes are out, the possibility of an eruption is getting more real."

Bali's disaster mitigation agency said 144,389 people had now been evacuated, compared to a tally of some 122,490 by Thursday.

They are staying in nearly 500 makeshift shelters in nine districts and some have crossed the Lombok Strait to take refuge on the neighboring island of Lombok.

Around 62,000 people lived in the danger zone before the evacuations, according to Indonesia’s disaster mitigation agency, but residents just outside the area have also left out of fear.

The airport in Bali's capital Denpasar, through which millions of foreign tourists pass every year, has not been affected, but several countries including Australia and Singapore have issued travel advisories warning visitors to exercise caution.

Mount Agung's last eruption more than 50 years ago killed nearly 1,600 people.