About 20,000 troops are being deployed in south-western Japan to help victims of a powerful earthquake that hit the region a day after an earlier tremor.
Rescue efforts are underway in the Kyushu region, and about 20,000 troops have been deployed, after the 7.3 magnitude-quake hit this morning (1.25am local time).
At least 15 people have been killed and hundreds injured, media reports said.
Dozens of people were feared trapped in the rubble of collapsed buildings.
The quake on Thursday killed nine people.
Roads have been damaged and big landslides have been reported over a wide area. Some 200,000 households were now without power.
A tsunami warning was issued, but was lifted 50 minutes later.
The extra troops were being sent to Kyushu to help police and firefighters.
"We are making every effort to respond," Chief Cabinet Secretary Yoshihide Suga said.
The second quake - which was at a depth of 10km near Kumamot - was much bigger and hit a wider area than the one that struck the city of Kumamoto on Thursday night.
Thousands of people spent the night on the streets and in parks - where they were huddled under blankets looking dazed and afraid.
There are many reports of people trapped inside buildings, including at least 60 inside an old people's home.
One village has been evacuated after a dam collapsed as a result of the quake, public broadcaster NHK said.
Japan's nuclear authority said the Sendai nuclear plant was not damaged.
A small eruption occurred at Mt Aso following the tremor, media reports said.
Gavin Hayes, a research geophysicist with the US Geological Survey in Colorado, told the BBC the latest earthquake would hamper the earlier rescue operation that was already under way.
He said more damage could be expected as the earthquake had been shallower and the fault-line had been much longer.
"The ground surface would have moved in the region of 4 to 5 metres. So, you are talking very intense shaking over quite a large area. And that's why we'll probably see a significant impact from this event."
Thursday's 6.2 quake caused shaking at some places as intense as the huge earthquake that hit the country in 2011, Japan's seismology office said.
That quake sparked a huge tsunami and a nuclear meltdown at the Fukushima power plant.
Most of those who died in Thursday's quake were in the town of Mashiki where an apartment building collapsed and many houses were damaged.
More than 1,000 people were injured.
Some 40,000 people initially fled their homes, with many of those closest to the epicentre spending the night outside, as more than 130 aftershocks had hit the area.
Aftershocks were continuing to hit the area, making the job of rescuing people even harder.
Japan is regularly hit by earthquakes but stringent building codes mean that they rarely cause significant damage.