A strong 6.3-magnitude earthquake hit western Japan early on Saturday, injuring at least 24 people and destroying some houses, officials and reports said.

Japan's meteorological agency, which earlier reported the quake was measured at magnitude 6.0, revised the seismic reading to magnitude 6.3. There was no risk of a tsunami, it said.

The quake struck at 5:33 am (2033 GMT on Friday) near Awaji island in the Seto Inland Sea southwest of the city of Kobe, the agency said, also revising the depth of the focus at 15 kilometres (9.3 miles).

The US Geological Survey also measured the tremor at 6.0 but at an even shallower depth of five kilometres.

It was the biggest earthquake to hit western Hyogo prefecture since 1995, when a 7.2-magnitude quake destroyed its port city of Kobe and killed more than 6,000 people.

But the damage was limited on Saturday, the National Police Agency said, although at least 24 people were injured.

An 82-year-old woman in Fukui prefecture suffered a broken leg after she fell to the ground, while another woman, 74, in Hyogo prefecture broke her hip bone, a police agency official said.

Japan's public broadcaster NHK showed footage of flattened brick walls and one house where all the roof tiles had collapsed to the ground.

Local train services were suspended for safety checks, while Kansai airport in Osaka Bay was temporarily closed, NHK said.

Kansai Electric Power said there was nothing untoward at its Oi nuclear power plant, currently the only one in Japan with reactors online.

"Our operation has continued as we haven't monitored any abnormality, but we are still checking if there is any damage to the facilities," a plant official said.

Japan is regularly hit by powerful earthquakes and has largely adapted its infrastructure to tremors that can cause widespread damage in other, less developed countries.

But in January 1995, a huge 7.2-magnitude quake hit the western port city of Kobe, burying residents in flattened buildings and uprooting highway overpasses and train tracks while fires raged through collapsed timber houses.

Hikaru Doi, a 36-year-old employee of a taxi company on Awaji island, told Jiji Press: "I was scared to death. I thought a big quake hit again."

In March 2011, Japan suffered a massive undersea quake with a magnitude of 9.0, which sent a towering tsunami into the northeast of the country, devastating coastal communities and killing nearly 19,000 people.

It also sparked the world's worst atomic accident in a generation when waves knocked out cooling systems at the Fukushima nuclear plant.

Japan turned off its 50 reactors in the wake of the Fukushima disaster but the two at the Oi plant resumed operations due to fears of a power shortage.