Even as efforts were redoubled to avert a meltdown and engineers struggled hard to fix power cables to restart water pumps, Japan`s Nuclear and Indistrial Safety Agency admitted that the cores at the plant`s No.1, 2 and 3 reactors had partially melted and radiation leaks were continuing.
The accident severity level at the plant was raised from four to five on the 7-point international scale by the agency, placing the crisis two levels below Ukrain`s 1986 Chernobyl disaster, a week after the magnitude-9 quake and massive tsunami rocked the country leaving over 17,000 people dead or unaccounted for.
The Chernobyl accident was caused by rupture of a reactor vessel followed by a series of explosions leading to a radioactive fallout that claimed the lives of over 4,000 people.
The reclassification of the severity level at the Fukushima plant also placed the crisis on par with the Three Mile Island accident in the United States in 1979.
"This is the largest crisis for Japan," Prime Minister Naoto Kan said during his meeting with visiting IAEA chief Yukiya Amano, adding that "every organisation (of the government)...is making all-out efforts to deal with the problem."
In a nationally televised address, Kan said he was confident that Japan will overcome the worst crisis since World War II and thanked the people for showing calm amd sought their cooperation in rebuilding the country.
Soon after arriving in Tokyo, Amano, a Japanese national who was accompanied by a four-member team of nuclear experts, said: "We see it (the nuclear crisis) as an extremely serious accident."
"The international community is extremely concerned about this issue, and it`s important to cooperate in dealing with it," he said, adding it was a race against clock.
The UN atomic watchdog has convened a meeting of its 35-member of board of governors on Monday in Vienna where Amano will them on his return from Japan.
Tokyo Electric Power Company (TEPCO), the operator of the nuclear plant, accelerated efforts to restore the lost cooling function of the reactors by reconnecting electricity to the site through outside power lines.
Some of the power distribution boards at the plant have been damaged by the quake-triggered tsunami and TEPCO will use makeshift replacement equipment.