Radiation levels in Tokyo, one of the world's most populous cities, rose 10 times above average

Radiation levels in Tokyo, one of the world's most populous cities, rose 10 times above average Tuesday evening, spreading fear among many of the 33 million residents in the metropolitan area.

The best advice experts could give them was to stay indoors, close the windows and avoid breathing bad air -- steps very similar to those for handling a smog alert or avoiding influenza.

While these steps may sound inconsequential, experts said the danger in Tokyo, while worrisome, is slight - at least for now.

"Everything I've seen so far suggests there have been nominal amounts of material released. Therefore, the risks are generally low to the population," Jerrold Bushberg, who directs programs in health physics at the University of California at Davis, said in a telephone interview.

"There may be more significant risks for emergency workers on site. They are dealing with the occupational exposure, but not for the population at large."

Fresh explosions Tuesday at the Fukushima plant, 180 miles north of Tokyo, released low levels of radiation, escalating a crisis triggered by last week's massive earthquake and tsunami. With cooling systems knocked out, the fear is more blasts within the reactors at the complex could eventually cause a major radiation leak.

The levels measured around Tokyo at one point were 40 times above normal but have receded to 10 times. That amounts to roughly the same dose as a chest or abdominal CT scan.