A 4.7-magnitude quake hit areas some 200 kilometres north of Tokyo today, but no tsunami was thought likely, Japan's meteorological agency said.
The quake hit Jetsu City and surrounding areas at 9:26am (0556 IST) at a depth of 20 kilometres, the agency said.
Around 20 per cent of the world's most powerful earthquakes strike Japan, which has developed one of the most sophisticated tsunami warning systems.
Just a moment before the quake struck, warnings for a strong tremor were flashed across television screens. There were no immediate reports of damage.