The quake struck at a relatively shallow depth of 17 kilometres 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 past year.
A 6.8-magnitude quake jolted waters near the Indonesian island of Sulawesi on Friday, according to the United States Geological Survey (USGS).
He added Sulawesi residents were advised to "evacuate as soon possible".
The quake was "strong and long lasting", Gina Saerang, a resident of Manado, the capital of North Sulawesi province, several hundred kilometers from the epicenter, said on social media.
"The agency is monitoring for high waves as the quake had the potential to trigger a tsunami", said Indonesian officials, which added that "the first wave may not be the biggest".
The quake was felt strongly in the nickel mining region of Morowali. Local residents were seen flooding the streets in panic following Friday's tremor.
In the twin quake-and-tsunami tragedy that hit Palu in September past year, high waves hit the shore after the tsunami warning had been lifted.
There were no immediate reports of casualties.
Both Japan and Indonesia on the Pacific "Ring of Fire" and is earthquake-prone.
Looping from New Zealand to Chile, around 90% of the world's earthquakes occur in this belt which is also home to more than 450 volcanoes.
The Pacific "Ring of Fire". "The initial jolt was followed a few minutes later by a 40-foot-high tsunami".
More than 2,000 people were killed. "A series of towering waves swept away thousands of people", says Smithsonian Magazine.