The strongest quake struck at 6.02pm local time (8.02pm AEST) on Friday and tsunami.
According to AFP reports, Facebook Live video showed long traffic jams formed in some parts of the region as terrified residents packed into cars, trucks and motorbikes to flee to higher ground following the tsunami warning.
Hospital patients after a powerful quake rocked the island of Sulawesi and triggered a 3-metre tsunami that swept away houses.
Indonesian TV showed a smartphone video of a powerful wave hitting Palu with people screaming and running in fear.
This natural disaster came after a series of strong quakes in August killed hundreds on the island of Lombok, south of Sulawesi.
At least one person was known to have died.
A powerful magnitude 7.7 quake which was centered in Donggala district, Central Sulawesi province, on Friday evening caused panic-stricken residents in neighboring Gorontalo province to stay outdoors. Such shallow quakes tend to be more destructive.
"When the [tsunami] threat arose yesterday, people were still doing their activities on the beach and did not immediately run and they became victims", Sutopo Purwo Nugroho, spokesman for BNPB, Indonesia's disaster response agency, told reporters in Jakarta, Reuters reported. People are running on the streets and buildings have collapsed.
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A search and rescue operation is now underway in Indonesia after a powerful quake and tsunami hit the island of Sulawesi.
Magnitude 7.5-quake launches tsnunami into Indonesian city of Palu with deaths and injuries unknown.
It's hit Palu, as well as the smaller city of Donggala and other coastal settlements. An official said widespread damage was expected and urged people to stay outdoors because of the danger of strong aftershocks.
United Nations spokesman Stephane Dujarric said United Nations officials were in contact with Indonesian authorities and "stand ready to provide support as required".
He said "many victims" were still to be accounted for.
Some 1,500 people were injured and about 400,000 residents were displaced after their homes were destroyed.
In December of 2004, the devastating "Boxing Day Earthquake" and ensuing tsunami killed 230,000 people across more than 10 countries.