The detection of high radiation was made at a water purification plant in the Japanese capital, prompting the Tokyo metropolitan government to issue a warning today that babies should not drink tap water.

Local authorities said 210 becquerels of radioactive iodine were detected per litre of water against the limit of 100 becquerels at a water purification plant yesterday in the Kanamachi district of Katsushika Ward, Kyodo news agency reported.

But the amount of the radioactive substance detected at the purification plant is lower than the 300-becquerel limit for people other than infants, it said.

In a survey of its three purification plants, the metropolitan government also detected 32 becquerels of the substance at a plant in Hamura in western Tokyo. However, the substance was not detected at another plant in Asaka, Saitama Prefecture.

Tokyo authorities said infants in the central 23 wards, plus 5 adjacent cities, should refrain from drinking tap water, national broadcaster NHK reported.

Premier Naoto Kan, meanwhile, warned consumers  against eating leafy vegetables such as spinach harvested in Fukushima, as radioactive materials far exceeding legal limits were found in vegetables in the region devastated by the March 11 earthquake of magnitude 9 and massive tsunami that left over 24,000 people dead or unaccounted for in Japan's northeast.

Kan instructed Fukushima Governor Yuhei Sato to ask people, including the prefecture's own residents, to refrain from eating vegetables such as cabbage, the "komatsuna" leaf vegetable, broccoli and cauliflower.

The order, which is based on findings by the Health Ministry that said radioactive materials in 11 Fukushima-produced vegetables surpassed legal limits set under the food sanitation law, will take effect "for the time being," government officials said.

It is the first time the government has issued a restriction on food intake in line with a special law for dealing with the nuclear disaster in Japan, whose Pacific coast in the northeast was shaken again by strong earthquakes today, including one measuring 6 on the Richter Scale.

Chief cabinet Secretary Yukio Edano said the warning was issued by the Prime Minister as a precautionary measure and denied the radiation levels could pose an immediate risk to human health.