TOKYO - A powerful 6.9 magnitude earthquake struck northern Japan on Saturday, causing strong tremors across Hokkaido island but no damage to several nuclear facilities in the region, officials said.
The quake, which was preceded by an early warning broadcast on television and radio, hit near the town of Obihiro at a depth of 103 kilometres (64 miles) at 11:17 pm (1417 GMT), according to US Geological Survey data.
Ten people suffered minor injuries due to falling objects, broken glass and other incidents, according to national broadcaster NHK, but authorities said no serious damage was reported and the quake did not generate a tsunami.
The shaking lasted about a minute, with video taken in the offices of NHK Hokkaido showing computer screens swaying and shelves threatening to give way.
Bottles smashed to the ground in supermarkets, some areas had power blackouts and a number of highways were closed. Trains were stopped on rural tracks as a precaution.
"Beware of possible landslides and buildings that could have been weakened," an official from Japan's Meteorological Agency warned at a press conference.
The most violent tremors were felt in the eastern part of Hokkaido -- the nation's second largest island and a popular skiing destination -- but the northern part of the island was also shaken along with parts of the main island of Honshu, where Tokyo is located.
Utility firms said no abnormalities were reported at the Tomari nuclear plant in Hokkaido's west, nor at the nuclear facilities in Aomori, the northernmost prefecture on Honshu.
Aomori is home to the Higashidori nuclear reactors and a nuclear reprocessing plant in Rokkasho, which is currently in a testing phase, as well as fuel storage sites.
At present only two of the country's 50 reactors are operational, after the entire network was shuttered over several months for scheduled safety checks following the quake-tsunami disaster of March 2011.
Both are in Oi, in Honshu's west.
Shortly before Saturday's quake hit, an alert was broadcast on television and radio through an early warning system established by the weather agency, and programmes were interrupted on NHK.
"Make yourself safe, turn off the gas, beware of falling objects, and if you are outside do not approach the coast," a broadcaster said.
Some four hours after the quake a 5.5-magnitude tremor struck off Japan's Izu islands, around 725 kilometres (450 miles) south of Tokyo, according to the US Geological Survey.
The devastating 2011 earthquake and tsunami in Japan's northeast left some 19,000 people dead or missing and crippled the Fukushima nuclear power plant in the world's worst atomic disaster in 25 years.
A powerful 7.3-magnitude undersea quake in the same area in December triggered a one-metre-high tsunami but there were no reports of fatalities.
Since the Fukushima disaster the country has been fearing another quake catastrophe.
Some of Japan's reactors, including the Higashidori facility, are built near faults suspected to be active.
The atomic energy issue has divided Japan, which used to rely on nuclear fuel for around a third of its electricity needs.
Meltdowns at Fukushima sparked fierce opposition to atomic power, sending tens of thousands of protesters onto the streets demanding a nuclear-free Japan.
Prime minister at the time Yoshihiko Noda pledged to phase out nuclear power by 2040. However, the wave of anti-atomic sentiment did not translate into success at the ballot box, with voters handing power to the Liberal Democratic Party -- seen as the most pro-nuclear party.
Observers widely expect Japan to restart its nuclear programme on the LDP's watch, with the government saying in December that it would review the previous administration's pledge to phase it out.
Operators must get permission from the newly formed Nuclear Regulation Authority (NRA) before their reactors can be restarted.
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