Disaster

Very, very bad news:

TOKYO — Japan faced the likelihood of a catastrophic nuclear accident Tuesday morning, as an explosion at the most crippled of three reactors at the Fukushima Daiichi Nuclear Power Station damaged its crucial steel containment structure, emergency workers were withdrawn from the plant, and a fire at a fourth reactor spewed large amounts of radioactive material into the air, according to official statements and industry executives informed about the developments.

“No. 4 is currently burning and we assume radiation is being released. We are trying to put out the fire and cool down the reactor,” the chief government spokesman, Yukio Edano, told a televised press conference. “There were no fuel rods in the reactor, but spent fuel rods are inside.”

Japan’s nuclear safety watchdog later said that the fire at the No. 4 reactor had been extinguished, The Associated Press reported.

Government officials also said the containment structure of the No. 2 reactor had suffered damage during an explosion shortly after 6 a.m. on Tuesday.

They initially suggested that the damage was limited and that emergency operations aimed at cooling the nuclear fuel at three stricken reactors with seawater would continue. But industry executives said that in fact the situation had spiraled out of control and that all plant workers needed to leave the plant to avoid excessive exposure to radioactive leaks.

If all workers do in fact leave the plant, the nuclear fuel in all three reactors is likely to melt down, which would lead to wholesale releases of radioactive material — by far the largest accident of its kind since the Chernobyl disaster 25 years ago.