Japan has reportedly decided to raise the severity level of the crisis at its tsunami-crippled Fukushima Daiichi nuclear power plant to the maximum seven on an international scale from the current status of five.

The Nuclear and Industry Safety Agency under the Ministry of Economy, Trade and Industry said the Japanese government decided to raise the level to the highest 7 on the International Nuclear Event Scale, which has so far only been applied to the 1986 Chernobyl catastrophe, Kyodo and NHK World reported citing official sources.

The Fukushima Daiichi nuclear plant was badly hit by the March 11 earthquake and tsunami that rocked Japan. The installation has been leaking radiation , despite efforts to cool and stabilise its reactors.

According to reports, the Nuclear and Industrial Safety Agency made the decision yesterday. It says the damaged facilities have been releasing a massive amount of radioactive substances, which are posing a threat to human health and the environment over a wide area.

The nuclear safety agency used the International Nuclear and Radiological Event Scale, or INES, to gauge the level. The scale was designed by an international group of experts to indicate the significance of nuclear events with ratings of 0 to 7.

On March 18th, one week after the massive quake, the agency declared the Fukushima trouble a level 5 incident, the same as the accident at Three Mile Island in the United States in 1979.

Until now, Level 7 has only been applied to the Chernobyl accident in the former Soviet Union in 1986 when hundreds of thousands of terabecquerels of radioactive iodine-131 were released into the air. One terabecquerel is one trillion becquerels.