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The quake hit at a depth of 35 kilometres (21 miles) at 0646 GMT, around 75 kilometres southeast of Gorontalo city, said Indonesia's Meteorology and Geophysics Agency.
"The quake's epicentre is on the sea but there's no tsunami potential," Indra, an agency official who uses only one name, told AFP, adding that no damage had been reported so far.
The US Geological Survey measured the quake at magnitude 5.8 and said it had a depth of 85 kilometres.
Indonesia sits on the Pacific "Ring of Fire", where the meeting of continental plates causes high seismic activity, and is frequently hit by earthquakes.