Japan has again detected "abnormal levels" of radiation in milk and spinach taken from areas near a quake-hit nuclear plant, government spokesman Yukio Edano said Sunday, urging consumers to stay calm.

The new tainted samples of milk were found at four sites in Fukushima prefecture, where the stricken power station is located, while one new contaminated sample of spinach was found in neighbouring Ibaraki, Edano said.

The announcement – the second in as many days – is certain to fuel public anxiety about the ongoing crisis at the Fukushima No. 1 plant, 250 kilometres (155 miles) northeast of Tokyo, and its impact on health.

But Edano insisted the public was not at risk.

"Even if (radiation) levels are superior, just because they are higher once, twice, over several days, this does not mean they pose health risks, even during a lifetime… So I would like everyone to stay calm," he told reporters.

The Fukushima nuclear plant was severely damaged by the 9.0-magnitude quake and tsunami on March 11. Radioactive substances have since leaked into the air.

Authorities in both prefectures are now checking where the products came from, how they were distributed and – depending on their findings – are ready to suspend sales.

Plant operator Tokyo Electric Power Co (TEPCO) on Saturday apologised for the contamination of foodstuffs and said it would look into compensating the farmers affected, Jiji Press reported.