Dangerous levels of radiation leaking from a crippled nuclear plant forced Japan to order 140,000 people to seal themselves indoors Tuesday after an explosion and a fire dramatically escalated the crisis spawned by a deadly quake and tsunami.

The international nuclear agency said a fire in a storage pond for spent nuclear fuel at the Fukushima Dai-ichi complex had released radioactivity "directly into the atmosphere".

In a nationally televised statement, Prime Minister Naoto Kan confirmed that radiation had leaked from the nuclear plant.

Though Kan and other officials urged calm, Tuesday's developments fueled a growing panic in Japan and around the world amid widespread uncertainty over what would happen next.

In the worst-case scenario, the reactor's core would completely melt down, a disaster that would spew large amounts of radioactivity into the atmosphere.

Tokyo reported slightly elevated radiation levels, but officials said the increase was too small to threaten the 39 million people in and around the capital, about 170 miles away. Closer to the stricken nuclear complex, the streets in the coastal city of Soma were empty as the few residents who remained there heeded the government's warning to stay indoors.

Officials just south of Fukushima reported up to 100 times the normal levels of radiation Tuesday morning, Kyodo News agency reported. While those figures are worrying if there is prolonged exposure, they are far from fatal.

Again, more devastating news from Japan, after an 8.9 magnitude earthquake and tsunami hit the island, causing nuclear reactors to smoke and leak. If the U.S. were hit with an earthquake of that magnitude, would our nuclear plants be able to sustain that force?

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