Japanese authorities have told the UN atomic watchdog there has been no release of radiation from a number of nuclear power plants affected by the massive 8.9 magnitude earthquake in Japan, the IAEA said on Friday.
Earlier, the International Atomnic Energy Agency's Incident and Emergency Centre had said that the four nuclear power plants closest to the quake which occurred near the east coast of Honshu, Japan, had been "safely shut down".
In an updated statement, the watchdog said that it had since received information from Japan's Nuclear and Industrial Safety Agency (NISA) that "a heightened state of alert has been declared at Fukushima Daiichi nuclear power plant."
NISA told the IAEA that the plant "has been shut down and no release of radiation has been detected."
Japanese authorities also reported a fire at the Onagawa nuclear power plant, but the fire "has been extinguished," the IAEA continued.
"The authorities say Oganawa, Fukushima-Daini and Tokai nuclear power plants were also shut down automatically, and no radiation release has been detected," it said.
The IAEA said that it had received information from the International Seismic Safety Centre that another tremor of magnitude 6.5 had been registered off the coast of Honshu, near the Tokai plant.
There have been dozens of powerful aftershocks since the first quake struck.
"The IAEA is seeking further details on the situation at Fukushima Daiichi and other nuclear power plants and research reactors, including information on off-site and on-site electrical power supplies, cooling systems and the condition of the reactor buildings," it said.
Nuclear fuel requires continued cooling even after a plant is shut down.
In addition, the IAEA said it was "also seeking information on the status of radioactive sources in the country, such as medical and industrial equipment."
The IAEA said that it had sent a so-called "offer of good offices" or assistance to Japan, "should the country request support."
And it added, "Current media reports say a tsumani alert has been issued for 50 countries ... The agency is seeking further information on which countries and nuclear facilities may be affected."
Earlier, Japanese Prime Minister Naoto Kan had also said that no radiation leaks have been detected from the nuclear plants following the quake.