'HORRIFYING'

President Joko Widodo was scheduled to visit evacuation centres on Sunday.

Australian Prime Minister Scott Morrison said Indonesia had not asked for help but he had contacted President Widodo overnight to offer support and deep sympathies.

“It is horrifying ... If he needs our help, he’ll have it,” he told ABC TV’s Insiders programme. 

More than half of the 560 inmates in Palu's prison escaped after its walls collapsed during the quake, according to state news agency Antara, while more than 100 inmates escaped from a prison in Donggala.

The military has started sending in aircraft with aid from Jakarta and other cities, authorities said.

Palu's airport was damaged in the quake, but was reopened for limited commercial flights on Sunday, authorities said.

Indonesia sits on the Pacific Ring of Fire and is regularly hit by earthquakes.

In August, a series of major quakes killed more than 500 people On the tourist island of Lombok, hundreds of kilometres southwest of Sulawesi.

Reuters