The Nuclear and Industrial Safety Agency and the Nuclear Safety Commission on Tuesday provisionally raised the severity level of the crisis at Tokyo Electric Power Co.'s stricken Fukushima No. 1 nuclear power plant from level 5 to the maximum 7 on the International Nuclear Event Scale — the same level designated for the world`s worst nuclear accident at Chernobyl in 1986.

NISA estimated that the amount of radioactive materials in terms of radioactive iodine-131 released into the air from the Nos. 1, 2 and 3 reactors at 370,000 terabecquerels (one terabecquerel being 1 trillion becquerels) and the NSC at 630,000 terabecquerels — far exceeding the criterion of tens of thousands of terabecquerels for level 7.

On March 18, NISA had provisionally set the level at 5, the same level as the Three Mile Island accident in 1979. Even after it became clear that the severity of Fukushima No.1's crisis exceeded that of the TMI accident, the government took such a long time before raising the level.