Partial meltdown hits Fukushima nuclear plant

Uranium fuel in at least one of the six reactors at Fukushima has melted, the operator of the crippled nuclear plant has said. The admission effectively torpedoes a plan to flood the overheating fuel with water and bring a quick end to the worst nuclear crisis since Chernobyl.

Tokyo Electric Power Co (Tepco) said water levels have fallen at least one metre below fuel rods inside Reactor 1 and that melted fuel has dropped to the bottom of the reactor's containment vessel. Engineers are working inside the reactor building for the first time since the crisis began when a hydrogen explosion blew off its roof following the huge quake and tsunami on 11 March.

Tepco general manager Junichi Matsumoto told reporters in Tokyo that the discovery means its timetable to entomb the containment reactor vessel in water may have to be scrapped. "We can't deny the possibility that a hole in the pressure vessel caused water to leak," Mr Matsumoto said.

Observers fear that Reactor 3, which contains MOX plutonium fuel, may have also suffered a meltdown, and the situation inside Reactor 2 is still shrouded in mystery.

"The situation is clearly far more serious than previously reported, and could escalate rapidly if the lava melts through the reactor vessel," warned Jan Beránek of Greenpeace.