Rescue workers conduct a search and rescue operation to a collapsed house at a landslide site caused by earthquakes in Minamiaso town, Kumamoto prefecture, southern Japan. (Reuters Photo)
The National Police Agency said 32 people had been confirmed dead in Saturday's quake. The government said about 190 of those injured were in a serious condition.
On the other side of the Pacific, Ecuador was also struggling with the aftermath of a major 7.8 quake which hit on Saturday, killing at least 28 people and sparking a tsunami warning.
Both Japan and Ecuador are on the seismically active "ring of fire" around the Pacific Ocean. Japan's 2011 quake and tsunami killed nearly 20,000 people.
The epicentre of Saturday's quake was near the city of Kumamoto and measured at a shallow depth of 10 km (six miles), the United States Geological Survey (USGS) said. The shallower a quake, the more likely it is to cause damage.
The city's 400-year-old Kumamoto Castle was badly damaged, with its walls breached after having withstood bombardment and fire in its four centuries of existence.
Bank of Japan Governor Haruhiko Kuroda, speaking at a G20 event in Washington, said it was too early to assess the economic impact but bank operations in Kumamoto were normal.
The USGS estimated there was a 72 percent likelihood of economic damage exceeding $10 billion, adding that it was too early to be specific. Major insurers are yet to release estimates.