Japan has raised its assessment of the accident at the Fukushima nuclear power plant to the most serious level on a 7-step international scale, equivalent to the 1986 Chernobyl disaster.

Japan’s nuclear regulator increased its assessment on the International Atomic Energy Agency scale – from the previous level 5 – because of the impact that radiation leaking from the plant would have on human health and the environment. Japan had initially classified the incident as a level 4 before later raising it to level 5.

While the new assessment puts the Fukushima Daiichi incident on a par with Chernobyl, the nuclear regulator said the amount of radioactive contamination that has escaped from the plant since it was damaged by Japan’s March 11 earthquake and tsunami was around one tenth of the radiation that escaped from the plant in the former Soviet Union.