An earthquake with a preliminary magnitude of 5.8 struck Fukushima Prefecture in Japan early Friday morning, Kyodo reported, quoting the Japan Meteorological Agency.
No tsunami warning has been issued, the news agency said.
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The focus of the quake was around 20 km (12.4 miles) underground in the prefecture, which hosts Tokyo Electric Power Co Inc's Fukushima Daiichi Nuclear Power Station, Kyodo said.
(Read more: Is nuclear disaster looming in Japan?)