Japanese authorities on Thursday detected rising levels of radioactive iodine at water purification facilities near Tokyo and officials have advised that tap water should not be given to infants to drink in the affected areas, sparking panic-buying of already scarce bottled water.

Local officials in Tokyo's neighboring Chiba Prefecture said they detected around 220 becquerels of radioactive iodine-131 per liter in the city of Matsudo's water supply on Wednesday.

The recommended maximum limit is 100 becquerels per liter for children under 1 year of age, and 300 becquerels for adults.

Radioactive iodine levels found at another purification plants in the region were also nearly double the recommended safe limit for infants at 180 becquerels per liter, the officials said.

Also bordering the Tokyo metropolitan area, local officials at the city of Kawaguchi in Saitama Prefecture said radioactive iodine rose to 120 becquerels per liter of water at its purification plant on Tuesday.

Following levels of iodine spiking to 210 becquerels on Tuesday at a purification plant serving the greater Tokyo area located in the Kanamachi district of the city, the Tokyo metropolitan government urged that tap water not be given to infants in the city's 23 wards and five surrounding cities.

But on Thursday levels of radioactivity dropped to 79 becquerels at the purification facility and the advisory against drinking tap water was dropped.

As authorities have also detected radioactive iodine in water supplies at levels between 103 and 245 becquerels, spanning from Ichikawa and Funabashi, to Ibaraki and Fukushima prefectures, panic-buying of bottled water has become rampant and threatened to deplete supplies.