The Tokyo Metropolitan Government says it has lifted restrictions against using tap water for consumption by infants in Tokyo's 23 wards and 5 adjacent cities, according to a report from public broadcaster NHK.

On Thursday, the Tokyo city authorities said water samples from the Kanamachi water purification facility had shown the level of iodine 131 falling to 79 becquerels a liter - below the acceptable limit of 100 for infants under 1 year old. Continued monitoring of the situation is essential, the officials said.

The advisory had been issued after levels above the limit were detected at the plant on Tuesday and Wednesday.

On Friday, the government plans to continue testing the level at the plant and distribute 240,000 bottles of water to households with infants, following similar distribution on Thursday, the NHK report said.

Meanwhile, an earthquake with a preliminary magnitude of 6.1 hit northern Japan on Thursday, NHK said.