The quake hit at 4:31 a.m. local time on Tuesday (1931 GMT Monday), 83 kilometers southwest of the city of Naha, the United States Geological Survey reported.
The tremor struck at a depth of 18 kilometers, the report added.
There were no immediate reports of casualties.
Earthquakes are common in Japan, which sits on the Pacific Ring of Fire, where the meeting of four tectonic plates causes high seismic activity.
A 9.0-magnitude earthquake and tsunami that struck Japan on March 11, 2011 left nearly 20,000 people dead or missing and crippled the cooling systems at the Fukushima nuclear plant, which caused meltdowns of three of its reactors.
GJH/HGL
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