The number of people believed missing from the quake and tsunami that struck Indonesia's Palu city has soared to 5,000, an official said Sunday, an indication that far more may have perished in the twin disaster than the current toll.

There are fears that two of the hardest-hit neighbourhoods in Palu - Petobo and Balaroa - could contain thousands more victims, swallowed up by ground that engulfed whole communities in a process known as liquefaction.