(CNN) -- A 6.8-magnitude earthquake early Saturday struck offshore not far from Fukushima, Japan -- the epicenter of a nuclear crisis following a massive 2011 earthquake and tsunami -- the Japan Meteorological Agency reported.
The same agency issued tsunami advisories for the Pacific coast in the region of Tohoku, as well as for coastal regions in Iwate, Miyagi and Fukushima prefectures following the quake. At one point, a tsunami warning was out for part of that area.
"Marine threat is in place," the meteorological agency cautioned for those in imperiled areas. "Get out of the water and leave the coast immediately."
According to the U.S. Geological Survey, the quake was centered off Honshu island some 129 kilometers (79 miles) east-southeast of Namie and 284 kilometers east-northeast of Tokyo. It was 13 kilometers, or 8 miles, deep.
The USGS initially had characterized this as a 6.8-magnitude quake, but a short time later downgraded it to a 6.5-magnitude. The Japanese agency stuck with its 6.8-magnitude measure.
There were no immediate reports of damage.
The Japan Meteorological Agency forecasts that, "though there may be (a) slight sea-level change in coastal regions, no tsunami damage is expected."
Any sizable tremor in or near Japan -- and any tsunami warning -- inevitably raises dark memories dating to March 11, 2011, when a 9.0-magnitude struck 231 miles northeast of Tokyo.
That quake, the fourth largest on record since 1900 and the largest ever to hit Japan, produced a tsunami with 30-foot waves
When all was over, the combination of the quake and, especially, the tsunami left some 16,000 people dead.
The event also set off a prolonged crisis at the Fukushima Daiichi nuclear power plant in the northern part of Honshu, including the spread of some radioactive material and very real fears of an even worse calamity as authorities tried to bring the dangerous situation under control.
CNN's Jessica King contributed to this report.
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