It was centered 21 miles (35 kilometers) beneath the ocean floor, the agency said.
Five aftershocks measuring more than magnitude 5 followed, the USGS said on its Web site.
The Indonesian Agency for Meteorology and Geophysics said in mobile phone text messages sent to reporters that the quake had the power to trigger a tsunami, but the warning was lifted about an hour later.
The agency received no reports from the field of injuries or damage, according to Soehardjono, who heads the agency's earthquake section in the capital, Jakarta. Like many Indonesians, Soehardjono goes by one name.
Grace Wakary, who lives in Manado, told The Associated Press she did not feel anything and that there had been no signs of panic in the city.
Indonesia is prone to seismic upheaval due to its location on the so-called Pacific "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.
In December 2004, a massive earthquake off the western island of Sumatra triggered a tsunami that battered much of the Indian Ocean coastline and killed more than 230,000 people - more than half of them in Indonesia's Aceh province. A tsunami off Java in 2007 killed nearly 5,000.
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