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Updated:

According to NHK, cooling equipment for the spent nuclear fuel pool in the reactor No. 3 of Tepco's Fukushima No. 2 power plant has stopped.

— The Japan Times (@japantimes) November 21, 2016

Subsequently, Reuters reported:

All Japan's nuclear power plants on the coast threatened by the tsunami are shut down in the wake of the March 2011 disaster, which knocked out Tokyo Electric Power Co's Fukushima Daiichi nuclear plant, spilling radiation into the air and sea.

A spokeswoman for Tokyo Electric Power, known as Tepco, said the cooling system for a storage pool for spent nuclear fuel at the reactor at its Fukushima Daini Plant had been halted. A spokesman said the cooling system had restarted soon after.

No other damage from the quake has been confirmed at any of its power plants, although there have been blackouts in some areas, the spokeswoman said.

Only two reactors are operating in Japan, both in the southwest. Even when in shutdown, nuclear plants need cooling systems operating to keep spent fuel cool.

Earlier:

A tsunami warning was issued and waves could come come ashore at any moment after a magnitude 6.9 earthquake struck in Japan just before 6am Tuesday morning (4pm ET Monday). Initial measurements put that quake at 7.3 on the Richter scale, but that was later downgraded

Asahi Shimbun reports:

There were no immediate reports of damage or injury, which struck at 5:59 a.m.

Tokyo Electric Power Co. was checking its nuclear plants in Fukushima for damage, public broadcaster NHK said. The utility could not immediately be reached by Reuters.

Tohoku Electric Power Co. said there was no damage to its Onagawa nuclear plant.

Television footage showed ships moving out to sea from Fukushima harbors, as the meteorological agency warned of a tsunami of 3 meters for Fukushima, where TEPCO's Fukushima No. 1 nuclear power plant was devastated in a March 2011 quake and tsunami.

Live stream from Japan:

Initial reports:

BREAKING: Magnitude 7.3 earthquake strikes off Fukushima in Japan, tsunami warning issued.

— The Associated Press (@AP) November 21, 2016

MORE: Tsunami warning issued after 7.3 magnitude Japan quake; residents urged to flee Fukushima coast - Japanese broadcaster

— Reuters World (@ReutersWorld) November 21, 2016

According to an initial report by the U.S. Geological Survey (USGS), the quake hit approximately 37 kilometers off the Japanese coast, east south-east from the city of Namie in the Fukushima prefecture just before 6am local time. The Japan Meteorological Agency, which issued the official tsunami warnings, reports the quake was relatively shallow, striking at a depth of approximately 10 kilometers.

In 2011, a major earthquake in a similar area triggered a massive tsunami that killed thousands of people and caused a meltdown at the Fukushima nuclear power plant.