An earthquake measuring 6.9 on the Richter scale has struck the Kyushu region of southern Japan. A tsunami warning has been issued in the region after Monday's earthquake. It was not immediately clear if there were any casualties or damage.

A 6.9-magnitude earthquake struck the Kyushu region on Monday, the Japan Meteorological Agency (JMA) said. A tsunami warning has been issued for Miyazaki and the southern prefectures of Kochi due to waves up to one meter high after the earthquake.

Japan's public broadcaster NHK reported that waves as high as 20 centimeters have already been recorded in the city of Miyazaki. About 400,000 people live in the provincial capital.

NHK said there were no reports of any unusual conditions at the Ikata nuclear power plant in western Japan or at the Sendai nuclear power plant in Kagoshima Prefecture. Two power plants are in operation near the area where the quake struck.

The Japan Meteorological Agency (JMA) has launched an investigation into whether the quake is related to the Nankai Trough. In August, a powerful earthquake of magnitude hit the region along the Pacific coast known as the Nankai Trough. Japan warned for the first time about a higher-than-normal risk after the quake.

Earthquakes are common in Japan. Japan is also one of the world's most seismically active areas. About one-fifth of the world's earthquakes of magnitude 6 or more occur in Japan.

Earlier on March 11, 2011, a strong earthquake of magnitude 9 hit the northeast coast of the country. It was the strongest earthquake in Japan's history. At that time, a major tsunami hit the country after the earthquake.