TOKYO (AFP) - A 6.1-magnitude earthquake struck off the south coast of Japan's main Honshu island on Sunday, the United States Geological Survey said, but no tsunami warning was issued.

The quake hit at 12:22 pm (1.22pm Singapore time), 644 kilometres south of Tokyo, at a depth of 424 kilometres, the USGS said.

Japan's Meteorological Agency said there was no risk of a tsunami.

Tokyo and its suburban Kanto region were rocked by minor tremors but there were no immediate reports of injuries or damage, the agency said.

"We have received no reports of damage to properties nor reports of injuries so far," a spokesman for the Tokyo Metropolitan Police Department said.

The area is prone to earthquakes.