The epicentre was located 230 kilometres (143 miles) southeast of the city of Shingu at a depth of 376 kilometres (233 miles).
According to nonprofit European-Mediterranean Seismological Centre (EMSC), the earthquake was felt as far as Minato, a special ward of Tokyo.
No further information on the possible casualties or damage has been reported.
The last severe earthquake in Japan occurred in 2011, when a magnitude 9.0 quake triggered a tsunami that later resulted in the Fukushima Daiichi nuclear disaster in which 19,749 people died, 6,242 were injured, and 2,556 went missing.