A strong 6.4-magnitude earthquake struck off northeast Japan's Fukushima region, home to a crippled nuclear power plant, early today, but there was no risk of a tsunami. The national Fire and Disaster Management Agency said the tremor at 3:54 am local time injured seven people but caused no damage to the Fukushima Daiichi plant, which was ravaged by a 9.0 quake and ensuing tsunami in March. According to the Japan Meteorological Agency, the tremor was presumed to be an aftershock of the March 11 quake. The US Geological Survey said the quake was centred in the Pacific around 100 kilometres south-southeast of Fukushima city, at a depth of about 40 kilometres. Meanwhile, heavy rains continued to lash northeastern Japan today with the death toll rising to three in the hardest-hit region of Niigata. Officials said three others were missing in Niigata and Fukushima. Thousands remained sheltered at evacuation centre to avoid floods from the rain storm since Wednesday following torrents that killed at least 59 people in South Korea last week. Local governments in Niigata and Fukushima had issued guidance since Friday to more than 60,000 people to flee their homes. In Fukushima, 1,020 were sheltered as of late yesterday and 2,278 houses had been flooded.