Indonesia’s Vice President Jusuf Kalla warned it could rise into the thousands.
Mr Kalla issued the warning on Saturday afternoon local time, pointing out there was “no word” yet from a city of 300,000 people.
Echoing the concern, the Red Cross said the lack of communication with the city of Donggala was “extremely worrying”.
“We’re now getting limited communications about the destruction in Palu city, but we have heard nothing from Donggala and this is extremely worrying,” a statement from the organisation said.
More than 600,000 people live in Donggala and Palu.
The Red Cross said its staff and volunteers were heading to the affected areas.
“This is already a tragedy, but it could get much worse,” it said.