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By Alexander Smith

Japan was shaken but relieved Tuesday after a powerful earthquake generated only a small tsunami that caused no apparent damage to nuclear facilities.

The magnitude-7.4 quake struck just 20 miles offshore from the Fukushima prefecture — the same stretch of coast devastated by a quake-generated tsunami in March 2011 that killed more than 18,000 people.

The quake, which struck at 6 a.m. local time (4 p.m. ET Monday), was in fact a long-delayed aftershock from the 2011 event according to the Japan Meteorological Agency. It put the magnitude at 7.4 but the United States Geological Survey (USGS) said it was a 6.9.

Fears were especially acute because the quake was just 20 miles from the Fukushima Daiichi nuclear plant, which suffered a meltdown and radiation leak after it was crippled by the 2011 quake.

All nuclear plants in the area have been shuttered since that incident, but the Tokyo Electric Power Company, or TEPCO, said that a cooling system for spent fuel at the nearby Fukushima Daini Plant had temporarily shut down because of Tuesday's quake.

This cooling system restarted after about an hour and a half and there were no "abnormalities," increased radiation levels, or injuries at either facility, according to TEPCO.

There were several reports of people being hurt by broken glass but all injuries were light, NHK reported citing the fire service.

Authorities had imposed tsunami warnings and advisories across the eastern Japanese coast that warned the wave could be some nine feet high. Coastal residents fled to higher ground and ships steamed out of the harbor in the city of Iwaki, fearing a repeat of 2011 when boats were dashed far inland.

The national broadcaster NHK flashed multiple warnings across its screens telling viewers: "Tsunami! Evacuate!" and "Please evacuate right now. Don’t stop, don’t try to go back."

However, the largest recorded wave was just 4.5 feet high, according to NHK, and no significant damage or deaths were reported. All tsunami warnings and watches were called off at 12:20 p.m. local time (10:20 p.m. ET Monday).

People gather at the mouth of a river Tuesday in Iwaki, Japan, after tsunami advisories were triggered by an earthquake.Kyodo via Reuters