The head of the International Atomic Energy Agency (IAEA), Yukiya Amano, called the situation at the Fukushima nuclear plant "very serious" on Wednesday as he prepared to fly to Japan.There have been fears of a meltdown at the plant ever since last week's magnitude-9 earthquake and ensuing tsunami disabled the cooling systems at all of the plant's reactors.
"The situation is very serious," Amano, who is Japanese said of the damages at the core of reactors 1, 2 and 3.
Nevertheless, with workers engaged in an-all out effort to stabilize the situation, Amano stressed that "it is not the time to say that things are out of control".
The IAEA director general said he would leave as soon as Thursday for a high-level meeting to explore further areas of cooperation between his agency and Japan, and to improve the flow of communication.
"There has certainly been room for improvement," he said.
A small group of IAEA experts were set to fly to Tokyo with Amano. Japan has requested experts to monitor the environmental situation around Fukushima.
The IAEA chief also said that there is not enough water in the reactor vessels to fully cover the hot nuclear material, and that temperatures have been rising at three ponds that store spent fuel.
Workers at Fukushima have battled to keep the reactors cool by injecting sea water to keep fuel rods submerged, but there have nevertheless been a series of explosions and fires at the complex.
White smoke was seen rising on Wednesday morning from reactor 3, after a fire broke out for a second day at reactor 4.
Elevated radiation levels at the plant Wednesday led to the temporary evacuation of the 50 workers who have been left behind. Plans to drop water on reactor 3 with helicopters were dropped.
The radiation rate dropped to 2.6 millisieverts shortly before 0300 GMT, down from around health-damaging 1,000 millisieverts observed overnight.
Chief cabinet secretary Yukio Edano said on Wednesday that the containment vessel of reactor 3 is unlikely to be severely damaged, stepping back from an earlier comment to the contrary, Japan's Kyodo news agency reported.