Japan raised the severity of its nuclear crisis at the Fukushima Daiichi nuclear plant to a level 7 from 5, putting it on par with the Chernobyl nuclear disaster in 1986. 
The rating reflects the initial severity of the crisis not the current situation which has seen radiation levels drop dramatically.
The operator of the crippled nuclear plant said that they are concerned that the radiation leakage could eventually exceed that of the 1986 Chernobyl nuclear disaster.
Japan is struggling to regain control of the Fukushima Daiichi nuclear plant after a massive earthquake and tsunami devastated its northeast on March 11, and is facing a major humanitarian and economic crisis.
The International Nuclear and Radiological Event Scale (INES) ranks nuclear incidents by their severity from 1 to a maximum of 7.
Here are some comments on the higher rating:
HIDEHIKO NISHIYAMA, A DEPUTY DIRECTOR-GENERAL AT JAPAN'S NUCLEAR and INDUSTRIAL SAFETY AUTHORITY (NISA)
We think it's very different from the accident in Chernobyl. First of all, the emission of radioactive substances is about 10 percent of the amount of Chernobyl. In the case of Chernobyl, 29 people died due to rapid absorption of massive radiation. That's not the case in Fukushima.
In the case of Fukushima, we had an explosion due to leaked hydrogen, blowing the roof off a building but the reactor containment vessel and reactor pressure vessel remains in the original shape, despite some leaks. In the case of Chernobyl, they could not keep working after the accident due to massive leaks of radioactive substances. In Fukushima, we still have engineers working to resolve the situation.
MURRAY JENNEX, ASSOCIATE PROFESSOR SAN DIEGO STATE UNIVERSITY
I think raising it to the level of Chernobyl is excessive. It's nowhere near that level. Chernobyl was terrible -- it blew and they had no containment, and they were stuck.
Their containment has been holding, the only thing that hasn't is the fuel pool that caught fire. I don't see those as the same event. If they want to do that, that's fine. I think they're being overly pessimistic.
KENJI SUMITA, OSAKA UNIVERSITY PROFESSOR
Raising the level to a 7 has serious diplomatic implications. It is telling people that the accident has the potential of causing trouble to our neighbours.
I think a level 7 is very extreme.
JAPAN'S NUCLEAR INDUSTRY AND SAFETY AGENCY (NISA)
According to the INES rating procedure, a provisional rating is given at the onset of an accident. The rating remains on a provisional status until the accident is deemed over, when a final rating is given upon analysis by a committee of experts. As for Daiichi the problems are still ongoing. This is a preliminary assessment, and is subject to finalisation by the International Atomic Energy Agency.
