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The quake hit at 9:23 am (0123 GMT) at a depth of 33 kilometres (21 miles), around 57 kilometres southwest of the main city of Palu, the US Geological Survey said.
"There was some shaking but no major panic in Palu. There's no report of casualty or injury so far," said Suharjono, technical chief at Indonesia's Meteorology and Geophysics Agency.
Indonesia sits on the Pacific "Ring of Fire", where the meeting of continental plates causes strong seismic activity including earthquakes and volcanic eruptions.