The Japanese government's worst-case scenario at the height of the nuclear crisis last year warned that tens of millions of people, including Tokyo residents, might need to leave their homes, according to a report obtained by The Associated Press. But fearing widespread panic, officials kept the report secret. The recent emergence of the 15-page internal document may add to complaints in Japan that the government withheld too much information about the world's worst nuclear accident since Chernobyl. It also casts doubt about whether the government was sufficiently prepared to cope with what could have been an evacuation of unprecedented scale. The report was submitted to then-Prime Minister Naoto Kan and his top advisers on March 25, two weeks after the earthquake and tsunami devastated the Fukushima Dai-ichi nuclear power plant, causing three reactors to melt down and generating hydrogen explosions that blew away protective structures.