Radiation has leaked from a Japanese nuclear reactor and authorities say there is a possibility of a meltdown at the Fukushima Daiichi plant about 250km north of Tokyo. But radioactive levels near the Fukushima nuclear plant, where five reactors were earlier under a state of emergency, have reduced since pressure built rapidly last night, said Japanese officials. The cooling system of the plant was damaged in the massive earthquake that struck northeastern Japan and triggered a tsunami, killing hundreds of people. More than 10,000 people remain missing in the port town of Minamisanriku, which has a total population of 17,000, said Japanese public broadcaster NHK. An explosion at the nuclear facility tore down the walls of one building on Saturday, leaving smoke billowing out. It was not clear if the damaged building housed the No. 1 reactor which officials fear could melt down. "We are now trying to analyse what is behind the explosion," Yukio Edano, a government spokesman, s