The airport in Palu city is reported to be closed.
An AP reporter saw bodies partially covered by tarpaulins and a man carrying a dead child amid the wreckage.
But the death toll is still unclear.
"The cut telecommunications and darkness are hampering efforts to obtain information,"' he said.
"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.
Indonesian President Joko "Jokowi" Widodo tweeted late on Friday evening: "At sunset an natural disaster hit Central Sulawesi and surroundings".
This handout photograph taken and released on September 28, 2018 by Indonesia's National Agency for Disaster Management shows a collapsed house following an quake in Donggala, Central Sulawesi.
A powerful natural disaster hit central Indonesia on Friday, causing a tsunami that slammed into a city on Sulawesi island with officials saying the tremor had levelled "many" buildings. A large mosque is one of the buildings which collapsed under the force.
A auto swept away by Friday's tsunami is seen stuck under a damaged building in Palu, Central Sulawesi, Indonesia.
A resident is seen beside the collapsed brick wall of her house at Tobadak village in Central Mamuju, western Sulawesi province, after a 7.5 magnitude quake hit the area.
The main shock rattled about three hours after a revised 6.0-magnitude quake jolted the area, killing one person and injuring 10 others with scores of houses damaged.
The quake triggered a tsunami that killed 230,000 people in a dozen countries.
The tsunami struck at the height of between 0.5 meters up and 3 meters, the head of the meteorology and geophysics agency Dwikorita Karnawati, told a press conference.
The tsunami warning for Central Sulawesi and West Sulawesi provinces were lifted an hour later, although officials now still fear further damage amid potential aftershocks.
Heart-thumping footage has emerged of an enormous tsunami flooding the shores of Palu, a city located on the Indonesian island of Sulawesi.
Some people climbed 6m trees to escape the tsunami and survived, Nugroho said.
"It was so strong".
The wire service said a reporter saw "numerous bodies in a hard-hit city", which "was strewn with debris from collapsed buildings".
"All the things in my house were swaying and the quake left a small crack on my wall", he said.
Daniel, a resident of Gorontalo district said he strongly felt the quake and asked all members of his family to stay outdoors.
Meanwhile, Foreign Minister Winston Peters is due to visit the region next week. Triggering a powerful tsunami.
The Ministry of Foreign Affairs says there are now 488 New Zealanders registered on SafeTravel as being in Indonesia.