An earthquake with a preliminary magnitude of 4.7 rocked areas along the Sea of Japan coast Sunday morning.
It measured lower 5 on the Japanese seismic intensity scale to 7 in the Joetsu region of Niigata Prefecture, the Meteorological Agency said, but no tsunami warning was issued and there were no immediate reports of injuries.
Residents should be wary of strong aftershocks in the next week or so because a series of tremors rattled the region earlier in the morning. The area was also shaken by a string of quakes measuring 4 to 5 in December 1990, it added.
The 9:26 a.m. quake registered lower 5 in Joetsu, 4 in Itoigawa, also in Niigata Prefecture, and 3 in the town of Toyono in Nagano Prefecture. The temblor was also felt in wide areas of central and eastern Japan.