The quake struck at a relatively shallow depth of 17 kilometres (10 miles) off the east coast of Sulawesi island, the USGS said, where a 7.5-magnitude quake-tsunami around the city of Palu killed more than 4,300 people last year.
Indonesia's disaster agency issued a tsunami warning for coastal communities in Morowali district, where residents were advised to move away from the coast.
The warning was later lifted by the agency, which had estimated the wave at under a half a metre (20 inches).
Video footage from Luwuk city showed scared residents -- some carrying children -- running from their homes and racing to higher ground on motorcycles.
The USGS warned that considerable damage was possible in poorly built or badly designed structures.
But it was not immediately clear how much damage was caused by the quake or if there were any casualties.
Hapsah Abdul Madjid, who lives in Luwuk city in Banggai district, Central Sulawesi, where the tremor was felt strongly, said people fled to higher ground and the electricity was cut, adding that residents panicked as fears soared over an imminent tsunami.
The tremor off the eastern coast of Sulawesi is on the other side of the island from disaster-hit Palu, where residents still felt the quake despite being hundreds of kilometres away.
"I ran straight outside after the earthquake -- everything was swaying," 29-year-old Palu resident Mahfuzah told AFP.
- Disaster prone -
Thousands in Palu were still living in makeshift shelters six months after the late September disaster with at least 170,000 residents of the city and surrounding districts displaced and entire neighbourhoods still in ruins, despite life returning to normal in other areas of the tsunami-struck city.
The force of last year's quake saw entire neighbourhoods levelled by liquefaction -- a process where the ground starts behaving like a liquid and swallows up the earth like quicksand.
Apart from the damage to tens of thousands of buildings, the disaster destroyed fishing boats, shops and irrigation systems, robbing residents of their income.
Indonesia has said the damage bill in Palu topped $900 million. The World Bank has offered the country up to $1 billion in loans to get the city back on its feet.
Indonesia is one of the most disaster-prone nations on Earth due to its position straddling the so-called Pacific Ring of Fire, where tectonic plates collide.
Last year was a particularly tough one, however, with more than 2,500 disasters ranging from a series of deadly earthquakes to killer landslides and volcanic eruptions.
The sprawling archipelago is dotted with more than 100 volcanoes, including one in the middle of the Sunda Strait between Java and Sumatra islands that erupted in late 2018 and unleashed a tsunami that killed more than 400 people.