The head of the International Atomic Energy Agency (IAEA), Yukiya Amano, said on Wednesday that he intends to fly to Japan as soon as possible, calling the situation at the stricken Fukushima nuclear plant "very serious", dpa reported.
There have been fears of a meltdown at the plant ever since a magnitude-9 earthquake and ensuing tsunami on Friday disabled the cooling systems at all of the plant's six reactors.
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.
Questions have also been raised on whether an inner containment shell at the plant's reactor number 3 has been damaged. The shell is one of three containment structures designed to prevent leakage of radioactive materials.
White smoke was seen rising Wednesday morning from reactor 3, after a fire broke out for a second day at reactor 4.
Elevated radiation levels at the plant on Wednesday led to the temporary evacuation of the 50 workers who have been left behind, along with the cancellations of plans to have helicopters drop water over reactor 3.
The IAEA has been planning to send a team of two experts to Japan to monitor the environmental situation and one official to coordinate with the Japanese government.
"The sooner, the better, in my view," Amano, who is from Japan, had said on Tuesday.