Flames and billows of black smoke poured from an electrical transformer at the Kashiwazaki nuclear plant, which automatically shut down during the quake.
The fire was put out shortly after noon and there was no release of radioactivity or damage to the reactors, officials said.
|The quake was centred around |
60km southwest of Niigata
Tsunami warnings sounded along affected costal stretches, with a surge of 50cm predicted, but they were later withdrawn.
The force of the quake buckled seaside roads and bridges, and one-metre-wide fissures opened up in the ground along the coastline.
Bullet trains in the area were also briefly halted and one train was derailed as it stopped at a station, although no injuries were reported.
Local TV said at least 12 people where trapped under collapsed houses in Kashiwazaki City, near the epicentre of the quake.
Water and gas services for Kashiwazaki's 35,000 households were suspended after reports of gas leaks, while nearly 24,000 households in the quake zone were without power as of Monday afternoon.
|The powerful quake forced a train |
off its tracks at one station [Reuters]
The tremor struck at 10:13 am (01:13 GMT) and was centred around 60km southwest of Niigata.
The focus of the quake was some 10km below the earth's surface, Japan's meteorological agency said.
NHK TV said there were power outages and that some highways had been closed.
Japan sits atop four tectonic plates and is one of the world's most earthquake-prone countries.
The last major quake to hit killed some 142,000 people in 1923, and experts say the capital has a 90 per cent chance of suffering a major quake in the next 50 years.
Meanwhile, a powerful typhoon that was expected to hit Tokyo skirted the capital and moved northeast after leaving three people dead and disrupting traffic.
Typhoon Man-Yi was losing strength on Monday morning as it passed southwest of Tokyo and later downgraded to a tropical storm with sustained winds of 83kph.