A moderate 5.9-magnitude earthquake struck off the south coast of the main Japanese island of Honshu, US geologists said on Monday, but no tsunami warning was issued.
The tremor, which hit just before midnight, hit at a depth of around 22 kilometres (14 miles), around 34 kilometres south of Shizuoka and 162 kilometres south of Tokyo, the US Geological Survey said.
The epicentre of the quake was a considerable distance from the 9.0 magnitude earthquake that rocked Japan on March 11, generating a massive tsunami that wiped out whole stretches of the country's northeast coast, leavving more than 20,000 people dead or missing.
Thousands more were made homeless when a nuclear reactor began melting down after its cooling systems were swamped by the waves in the worst atomic disaster the world has seen for a quarter of a century.
Japan, located at the junction of four tectonic plates, experiences 20 percent of the strongest quakes recorded on Earth each year.