Japan's Nuclear Safety Agency has raised the nuclear alert level of the Fukushima Daiichi power plant to seven from the previous rating of five, the highest on the international scale for nuclear accidents.
This is the same rating as the Chernobyl accident in 1986.
But Japanese officials say this does not mean the Japanese plant poses the same level of threat as the disaster in Ukraine.
[Interview : Hidehiko Nishiyama, Spokesman
Japan's Nuclear & Industrial Safety Agency
] "Based on data we've collected since March 18th, we've given this a preliminary rating of seven. However, the emission of radioactive substances is 10 percent of the amount of the Chernobyl incident, which is rated at a similar level."
Meanwhile, another powerful aftershock hit northeastern Japan Tuesday afternoon, rattling parts of Fukushima and Ibaraki prefectures, but no one was killed.
The 6.3 magnitude quake hit the coastal region of Fukushima at 2:07 p.m. and was felt 200 kilometers away in Tokyo at a magnitude of 3.0.
TEPCO the operator of the Fukushima Daiichi nuclear complex said its employees at the plant were temporarily evacuated.
No further damage has been reported there.
And nuclear industry experts and government officials from Korea and Japan started a 2-day meeting in Tokyo on Tuesday.
The experts discussed topics such as nuclear plant safety measures and recording radiation levels, and vowed nuclear cooperation between the two countries.
The final results of the meeting will be announced on Wednesday morning.
Kim Han-ul, Arirang News.