The quake, which struck at 10:52 a.m. (2152 GMT on Tuesday), was located 175 miles (282 km) southwest Fiji's capital, Suva, at a shallow depth of 9.4 miles (15 km), the USGS said.
The Pacific Tsunami Warning Centre initially issued a local tsunami warning and said that hazardous tsunami waves were possible and could strike the coastline of Fiji by 11:45 a.m. (2245 GMT on Tuesday), but then rescinded the threat soon after.
"We felt it ever so slightly in Suva," Sune Gudnizt, head of the United Nations' Office for the Coordination of Humanitarian Affairs told Reuters by telephone.
Radio New Zealand reports that people have been evacuating Nadi since the earthquake, Fiji's tourism hub.
Australia faces no threat of a tsunami from the powerful quake.
"We often get some very deep earthquakes there which don't pose too much of a problem, but in this case there is potential for a small local tsunami in that area," Geoscience Australia's Jonathan Bathgate told ABC Radio.
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