Here's what is happening now...
Tokyo (CNN) -- A white cloud of smoke or steam rising above Japan's Fukushima Daiichi nuclear plant on Wednesday may have been caused by a breach in the containment vessel in one of its reactors, government officials said.
Chief Cabinet Secretary Yukio Edano said a breach in the No. 3 reactor's containment vessel -- the steel and concrete shell that insulates radioactive material inside -- may have brought about the smoke.
Officials asked workers at the plant to evacuate temporarily earlier Wednesday after the smoke rose above the plant and radiation levels spiked. Authorities later allowed them to return after radiation levels fell, the Tokyo Electric Power Company said.
Radiation levels at the plant have surged and dropped repeatedly over the past few days. The most recent spike "probably" occurred "because the containment vessel in reactor No. 3 has been damaged," a spokesman for Japan's nuclear safety agency later told reporters.
Earlier in the day, officials spotted a fire in the plant's No. 4 reactor building. But 30 minutes later, flames were no longer visible, the Tokyo power company said.
Photographs of the building released by the power company Wednesday showed a massive hole in a wall and significant deterioration in the roof.
News of the blaze renewed concern over spent fuel rods sitting in an uncovered pool inside, which would release dangerous radiation if they caught fire.
"Each time there was one of these fires, the danger to those spent fuel ponds increases, because they're not contained. ...If they are compromised, it would be very serious indeed," said James Walsh, a CNN contributor and research associate at the Massachusetts Institute of Technology's security studies program.
Agency: Damaged container may be causing smoke, radiation spike - CNN.com
I haven't seen any news articles or reports claiming that deadly radiation is threatening Tokyo.
