Updated 2:03 p.m. ET

 

SOMA, Japan - 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 tsunami.

 

In a nationally televised statement, Prime Minister Naoto Kan said radiation had spread from the four stricken reactors of the Fukushima Dai-ichi nuclear plant along Japan's northeastern coast. The region was shattered by Friday's 9.0-magnitude earthquake and the ensuing tsunami that is believed to have killed more than 10,000 people, plunged millions into misery and pummeled the world's third-largest economy.

 

Workers were struggling to prevent meltdowns of three reactors at the site when the fourth reactor blew, reports CBS News correspondent Harry Smith. The fire that followed is believed to be the source of elevated radiation readings at the site earlier in the day.

 

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