Japan earthquake: Rescue under way after 7.3 tremor

These are the biggest earthquakes to hit Kumamoto in nearly 100 years

Rescue efforts are under way in south-western Japan to help victims of a powerful earthquake that hit the region a day after an earlier deadly tremor.

Some 20,000 troops are being deployed in the operation in Kyushu region after the magnitude-7.3 quake at 01:25 on Saturday (15:25 GMT Friday).

At least 18 people have been killed and hundreds injured, media reports say.

Dozens of people are feared trapped in the rubble of collapsed buildings. The quake on Thursday killed nine people.

In pictures: Japan earthquake

Roads have been damaged and big landslides have been reported over a wide area. Some 200,000 households are now without power.

There are fears that forecast rain could set off more mudslides.

Collapsed dam

The extra troops are 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 (six miles) near Kumamoto - was much bigger and hit a wider area than the one that struck the city of Kumamoto on Thursday night.

Kumamoto prefectural official Tomoyuki Tanaka told AP that the death toll was climbing by the hour.

Kumamoto resident Gary Irwin says many people have been sleeping in cars for safety

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 says.

A number of buildings in the region collapsed or were severely damaged after the quake

Members of Japan's self-defence forces are helping police and firefighters in the rescue operation

A number of residents have been evacuated from the city of Kumamoto - one of the worst hit areas

Japan's nuclear authority said the Sendai nuclear plant was not damaged.

A small eruption occurred at Mt Aso following the tremor, media reports say.

Gavin Hayes, a research geophysicist with the US Geological Survey (USGS) 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 4-5m (yards). 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."