It is the unanimous opinion of US scientific experts on the ground in Japan that, while the situation at the Fukushima Daiichi nuclear power plant remains serious and dynamic, the health and safety risks to areas beyond the 50-mile evacuation zone are low and do not pose significant risks. This includes the cities of Tokyo, Nagoya, Yokohama, etc.
Even in the event of an unexpected disruption at the plant, harmful exposures to people beyond the 50-mile evacuation zone are highly unlikely, and there would be a significant amount of time to assess steps to be taken.