Japan hit by 6.9 quake near feared Nankai Trough region

The JMA was investigating whether the quake was related to the Nankai Trough, NHK said.

The Nankai Trough, where the Philippine Sea Plate is subducting under the Eurasia Plate at the bottom of the sea off the southwest coast of Japan, produces massive earthquakes about every 100-150 years. 

Strong quakes nearby are seen as a potential indication that a megaquake could be more likely.

The JMA in August issued a week-long advisory for a "relatively higher chance" of a megaquake as powerful as magnitude 9 after a magnitude-7.1 quake hit the country's southwest.

After Monday's quake, tsunami advisories for waves of a maximum height of a metre were issued for the southern prefectures of Miyazaki and Kochi. 

A 20cm tsunami was later recorded reaching Miyazaki city, public broadcaster NHK reported.

There were no abnormalities reported at the Ikata Nuclear Power Plant in western Japan or the Sendai Nuclear Power Plant in Kagoshima prefecture, NHK said, referring to the two plants nearest to where the quake occurred.