Engineers were no closer to restoring the cooling systems at the plant's reactors, critical to bringing down the temperature of overheated nuclear fuel rods, showing that the battle to contain the damage was far from over, although a fire at the plant appeared to have been extinguished.

The rating of the accident at the Fukushima Daiichi nuclear plant was raised to 7, the worst on an internationally recognized scale, from a 5-rating. Japan said this reflects the initial severity of the crisis and not the current situation.

"This is a preliminary assessment, and is subject to finalization by the International Atomic Energy Agency," said an official at the Nuclear and Industrial Safety Agency (NISA), the government's nuclear watchdog, which made the announcement with the Nuclear Safety Commission.

Reuters