The evacuation at the Fukushima nuclear complex has temporarily stopped efforts to bring the radiation leaking plant under control.
In the meantime, that radiation is spreading.
Tap water in Tokyo has tested two times above the limit safe for infants. Radiation has also been found in produce, milk and seawater.
"It is really scary. It is like a vicious negative spiral from the nuclear disaster," said Etsuko Nomura, a mother of two young children ages 2 and 5. "We have contaminated milk and vegetables, and now tap water in Tokyo, and I'm wondering what's next."
Infants are particularly vulnerable to radioactive iodine, which can cause thyroid cancer, experts say. The limits refer to sustained consumption rates, and officials urged calm, saying parents should stop giving the tap water to babies, but that it was no worry if the infants already had consumed small amounts.
They said the levels posed no immediate health risk for older children or adults.
The crisis is emerging as the world's most expensive natural disaster on record. Japan's government says the economic cost of last week's earthquake and tsunami could reach $309 billion.
The death toll has now topped 9,400, and more than 15,600 people are still listed as missing.
The Associated Press contributed to this report.