A magnitude 4.7 earthquake shook Niigata prefecture in central Japan Thursday but there were no immediate reports of injuries, meteorologists said. The quake reported just after 11 a.m. local time was centered in the town of Toka but there were no tsunami threats, Kyodo News reported. Tokyo Electric Power Co. was quoted as saying the Kashiwazaki-Kariwa nuclear power plant in the prefecture was operating normally after the quake. Japan has been battling its worst nuclear power crisis at the Fukushima Daiichi nuclear plant in the Fukushima prefecture in the northeast region of the country since March 11, when the plant was struck by a magnitude 0 earthquake followed by a monstrous tsunami that killed thousands of people.