The AP reports:
TOKYO, Japan -- The walls of a building at nuclear power station crumbled Saturday as smoke poured out and Japanese officials said they feared the reactor could melt down following the failure of its cooling system in a powerful earthquake and tsunami.
It was not clear if the damaged building housed the reactor. An official said the utility that runs the Fukushima Daiichi plant was reporting that several workers may have been injured.
Japanese officials fear a meltdown,but it's not known if the reactor has been breached. Here's footage of the BBC airing the moment of explosion.
Japanese TV first aired shots of smoke from the explosion:
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UPDATE: BBC has a more alarming report::
Huge blast at Japan nuclear power plant
A massive explosion has struck a Japanese nuclear power plant after Friday's devastating earthquake.
A huge pall of smoke was seen coming from the plant at Fukushima and several workers were injured.