Japan's government on Friday asked people still living within 20-30 kilometres (12-18 miles) of the stricken Fukushima nuclear plant to leave voluntarily, after it earlier told them to stay indoors.

Hundreds of thousands of residents were evacuated from within a 20 km radius of the plant in the days after it was damaged by the March 11 earthquake and tsunami which disabled its crucial cooling systems.

As radioactive steam and smoke have wafted from the crippled site, and as hundreds of workers have battled to stabilise it, several foreign governments have urged their citizens to leave areas within 80 or even 100km of the plant.

Japan's top government spokesman on Friday asked people remaining within the 30km zone to leave voluntarily, urging them to do so both for their own comfort and because radiation contamination may increase.

"It has become difficult for them to get daily necessities because the distribution of goods has stagnated," said Chief Cabinet Secretary Yukio Edano.

"It is desirable that they voluntarily evacuate. I cannot rule out the possibility that the government will issue an evacuation order for this area if the radiation level goes up further."

earlier related report
Tokyo-grown vegetable shows high radiation
Osaka (AFP) March 25, 2011 - Radiation above the legal limit has been detected in a vegetable grown in Tokyo, Japan's health ministry said, amid a deepening food scare that has seen some imports from the country banned.

The level of radiation found in a sample of Komatsuna, or Japanese mustard spinach, was 890 becquerels per kilogram, exceeding the legal limit of 500, the ministry said.

It is the first time radioactive caesium exceeding the legal limit has been found in a Tokyo vegetable, public broadcaster NHK said.

Two weeks after Japan was crippled in the March 11 earthquake and tsunami, the crisis at the Fukushima nuclear plant northeast of Tokyo remains unresolved.

With the plant emitting radioactive materials, higher levels of radiation have been found in nearby farm produce and Japan has stopped the shipment of those vegetable and dairy products.

Tokyo's drinking water hit unsafe levels for infants this week amid the global food scare.

The ministry said that the radioactive caesium was detected on Thursday in the leafy green Komatsuna taken from a field in Edogawa ward on Wednesday.

It had been grown at a research centre and is not being sold on the market. The level of radioactivity would not have an adverse effect on health, even if the vegetable was eaten, the report said.

On Friday South Korea and the EU joined the United States, Russia and several other countries in restricting food imports.

Higher radioactivity has also been detected in the ocean near the Fukushima plant on Japan's Pacific coast, raising public fears about the safety of fish and seaweed, which are traditional staples in the island nation's diet.