Traces of radioactive substances have been detected in Japan's tap water following an emergency at a quake-hit nuclear plant, but are not a risk to human health, the government said.
Abnormal levels of radioactive iodine were found in the water supply in Tokyo and also in Fukushima prefecture, home to the plant located some 250 kilometres (155 miles) northeast of the capital, officials said.
Such readings were also made in the central prefectures of Gunma, Tochigi, Saitama, Chiba and Niigata.
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Traces of radioactive caesium were also found in tap water in Tochigi and Gunma, the officials said. But these levels were also well within the safety standards for drinking water, they added.
In the Fukushima town of Kawamata, 45 kilometres from the plant, the level of iodine-131 in water was 308 becquerels per kilogramme on Thursday, 155 on Friday and 123 on Saturday, the health and welfare ministry said, demonstrating levels were going down.
The level of 300 becquerels per kilogramme is set as a threshold where the government considers advising people to limit the intake of water, ministry official Yusei Kobayashi said.
This limit is one fourteenth of an amount of radioactivity which a person is exposed to by travelling from Tokyo to New York by air, he said.
Levels of iodine-131 were far lower elsewhere - 77 in Tochigi and 1.5 in Tokyo, the education and science ministry said.
Earlier, the government said it had discovered abnormal levels of radiation that exceeded the legal limit in milk and spinach from areas near the stricken plant, but they posed no immediate threat to humans.
The findings are nevertheless likely to fuel consumer fears in the wake of a March 11 quake and tsunami which critically damaged the Fukushima No.1 plant, sending radioactive substances leaking into the air.
