New Zealand officials are organising for iodine tables to be stockpiled at the nation's embassy in Tokyo.
The move comes as radioactive iodine detected in Tokyo's water supply prompted Japanese authorities to warn that infants in Tokyo and surrounding areas should not be given tap water to drink, adding to the anxiety about public safety posed by Japan's nuclear crisis.
Australian officials in Japan are reported to have already distributed protective medication to hundreds of their own citizens in areas of northern Honshu affected by radiation from the stricken Fukushima nuclear power plants.
The principal elements that have been released from reactors there are short-lived iodine 131 - a severe risk for triggering thyroid cancer - and very long-lasting caesium 137, which travels easily through the food chain.
A spokeswoman for the Ministry of Foreign Affairs in Wellington said New Zealand's National Radiation Laboratory had advised that iodine tablets were only required when there was a risk of exposure to hazardous doses of radioactive iodine.
"Some people in Japan are currently being given iodine tablets (potassium iodide or potassium iodate) as a precaution in case the situation significantly worsens," she said.
"As a precautionary measure, additional stocks are being sourced for potential future distribution by the New Zealand Embassy in Tokyo."
Potassium iodide can protect the thyroid gland by saturating it with normal iodine so it will have no need to soak up the radioactive form. But the spokeswoman said that iodine tablets should only be taken on instruction from the Japanese authorities or New Zealand's Ministry of Health, and people should not otherwise self-medicate with products containing iodine unless directed by a doctor.
"The New Zealand Government is keeping the situation under constant review," she said.
Pregnant women, nursing mothers and fetuses, as well as children, face the greatest danger from radioactive iodine, which is taken in by the thyroid gland and can cause thyroid cancer.
Children are at much higher risk than adults because they are growing, and their thyroid glands are more active and in need of iodine.
Iodide tablets must be taken at least an hour before exposure or within 24 hours of exposure, and then every 24 hours until the danger has passed. They only protect the thyroid, and offer no protection against other radionuclides such as caesium.