A tsunami warning for a wave measuring one metre was issued after the earthquake on Tuesday.
The Japanese government issued emergency earthquake warnings for Kumamoto, Nagasaki, Kagoshima, Fukuoka, Saga, Oita, and Miyazaki prefectures, all on Japan's southern Kyushu island.
Australia's Bureau of Meteorology said there were no tsunami threat to the country's mainland, islands or territories.
Japan is one of the world's most earthquake-prone countries, with a tremor occurring at least every five minutes.
Located along the "Ring of Fire" of volcanoes and oceanic trenches partly encircling the Pacific Basin, Japan accounts for about 20 per cent of the world's earthquakes of magnitude 6.0 or more.
Kyushu Electric Power said there were no reports of irregularities at its Sendai and Genkai nuclear power stations after the earthquake.
Train operator JR Kyushu said it had suspended services, including its high-speed Shinkansen trains following the quake.
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