The quake struck at a depth of 24 kilometres and was centred in the Molucca Sea between north Sulawesi and north Maluku, according to the USGS.
Indonesia's geophysics agency issued a tsunami warning for coastal communities nearby.
There were no immediate reports of damage or casualties, but residents in the city of Ternate in North Maluku province described the panic when the quake hit.
"I was getting ready to sleep when the window started rattling," resident Budi Nurgianto told AFP.
"It was very strong -- I ran from my house and all my neighbours fled too." According to the USGS, considerable damage was possible in poorly built or badly designed structures.
Indonesia is one of the most disaster-hit nations on Earth due to its position straddling the so-called Pacific Ring of Fire, where tectonic plates collide.
It has been hit by a string of deadly quakes including a devastating 2004 tremor measuring 9.1 magnitude that struck off the coast of Sumatra and triggered a tsunami that killed 220,000 throughout the region, including 168,000 in Indonesia.
The Boxing Day disaster was the world's third biggest quake since 1900, and lifted the ocean floor in some places by 15 metres (50 feet).
Indonesia's Aceh province is the hardest hit area, but the tsunami affects coastal areas as far away as Africa.
Last year, a 7.5-magnitude quake and a subsequent tsunami in Palu on Sulawesi island killed more than 2,200 with a thousand more declared missing.