A fresh earthquake measuring 5.4 has hit southern Kyushu island on Saturday morning, following a 7.3-magnitude quake that killed at least six people overnight.
Kumamoto Prefectural official Tomoyuki Tanaka says the death toll is still unclear, with the fire department reporting a higher number of at least seven.
More than 400 people are reported injured.
Japanese TV news footage showed collapsed and flattened houses, and said people are trapped in buildings.
The Japan Meteorological Agency gave a preliminary reading of magnitude-7.3 for the temblor that struck early Saturday. A magnitude-6.5 quake struck late Thursday, killing 10 people. Aftershocks are rattling various areas in Kyushu, one of Japan's main four islands.
The magnitude-7.3 quake shook the Kumamoto region at 1:25 a.m. killing at least six people. On Thursday night, the area was hit by a magnitude-6.5 quake that left 10 dead and more than 800 injured.