The AP News app just beeped my iPhone that Japanese officials have confirmed an explosion at the Number 3 reactor of the Fukushima Daiichi nuclear power plant. It was a building at the Number 1 reactor that exploded yesterday. More details as they come in.
UPDATE: From the BBC:
A second explosion has hit the nuclear plant in Japan which was damaged in Friday’s earthquake, but officials said it had resisted the blast.
TV footage showed smoke rising from Fukushima plant’s reactor 3, a day after an explosion hit reactor 1.
Japan’s nuclear safety agency said the blast was believed to have been caused by the build-up of hydrogen.
However, the agency said it could not confirm whether there had been an uncontrolled leak of radioactivity.
UPDATE, UPDATE: There are some in the comment thread who seem to think that I am being alarmist… that it was just a hydrogen explosion, so nothing to worry about. But I dunno, it’s hard to watch a mushroom cloud rise over a nuclear power plant and not be at least the teensiest bit concerned:

@52
Yes.
Also, these meltdowns ARE RACIST.
😉
Did I link that cool Godzilla vid for you guys yet?
OMG you guys switched to the “Continue Reading” expander like they use on The Daily Dish! I could kiss you!
@48
You could at least use my entire sentence when your criticising me.