(AFP)--A strong 6.4-magnitude earthquake hit Japan's southwestern island of Kyushu on Thursday, collapsing homes and sparking at least one fire, officials said, but the scale of damage remained unclear.
The quake struck at 9:26 pm (1226 GMT) in Kumamoto prefecture, central Kyushu, at a relatively shallow depth of 10 kilometres (6.2 miles), the Japan Meteorological Agency said, which said there was no danger of a tsunami.
The quake was followed about 30 minutes later by a smaller one with a magnitude of 5.7, the agency said.
The stronger quake was measured at 6.2 by the US Geological Survey, which put the second quake at 5.4. Another smaller aftershock followed.
Japanese Chief Cabinet Secretary Yoshihide Suga, the government's top spokesman, said officials had information suggesting some houses had collapsed and were working to collect information.
"We are doing our best for emergency disaster measures by prioritising efforts to save and rescue victims," he said.
"I ask people in the disaster zone to act calmly and help each other."
Japan's public broadcaster NHK also reported that some buildings had collapsed in the town of Mashiki on Kyushu with people possibly trapped underneath.
NHK showed a what appeared to be a house in flames as firefighters attempted to douse it with water.
Cameras showed violent shaking in the city of Kumamoto at the time of the quake, which was felt throughout Kyushu.
Japanese media reported that shinkansen -- bullet train -- services were halted on the island.
NHK also showed some damage including lumps of broken concrete on a street in Kumamoto prefecture. Residents stood outside making calls on mobile phones.
An official at the Sendai nuclear plant in Kyushu, who declined to be named, said the plant was operating normally but that officials were checking for any abnormalities.
NHK showed residents in Kumamoto prefecture taking refuge outside, saying that the quake's shaking was intense and had caused some power outages.
Japan sits at the junction of four tectonic plates and experiences around 20 percent of the world's most powerful earthquakes.
But rigid building codes and strict enforcement mean even powerful tremors frequently do limited damage.
A massive undersea quake that hit on March 11, 2011, sent a tsunami barrelling into Japan's northeast coast, leaving about 18,500 people dead or missing, and sending several reactors into meltdown at the Fukushima nuclear plant in the worst atomic accident in a generation.