TOKYO - Japan's weather agency warned of another strong earthquake after a 6.9-magnitude temblor struck the Kyushu region in southwestern Japan on Monday.

The strong temblor occurred at 9:19 pm local time, measuring a lower 5 on the Japanese seismic scale of 7 in the hardest-hit areas, according to the Japan Meteorological Agency (JMA), with no immediate reports of injury or damage.

At a depth of approximately 30 km, the epicenter was located off the waters of Hyuga-nada in Miyazaki prefecture at a latitude of 31.8 degrees north and a longitude of 131.6 degrees east, the JMA added.

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The magnitude of the quake was revised from an initial report of 6.4.

A Tsunami with heights of around 20 cm was observed in part of Miyazaki prefecture and 10 cm in some areas in Kochi prefecture after the JMA issued a tsunami advisory for the two prefectures.

No abnormalities were detected at the Ikata nuclear power plant in Ehime prefecture and the Sendai nuclear power plant in Kagoshima prefecture, according to the operators.

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A weather official said at a news conference that Monday's tremor is not directly linked to the risk of a megaquake that is expected to strike the Nankai Trough in the seas off central through southwestern Japan.

The JMA had previously issued a Nankai Trough megaquake alert that remained in place for one week after a magnitude 7.1 quake struck off the coast of Kyushu in August last year.