A magnitude 7.4 earthquake struck southern Japan early on Saturday morning (local time), triggering a tsunami advisory.

The quake's epicentre was near the city of Kumamoto and measured at a depth of 40 km, the US Geological Survey said.

The USGS minutes earlier reported a 7.1 quake with a depth of 7 km close to the same location.

The Japan Meteorological Agency issued a tsunami advisory, which identifies the presence of a marine threat and asks people to leave coastal regions, for the Ariake and Yatsushiro seas.

Local broadcaster NHK said the advisory suggested a possible wave of one metre in height.