TOKYO - Samples of rice grown in a town near Tokyo showed no radioactive materials when tested, officials said on Wednesday, a relief for farmers preparing to ship Japan's traditional food staple.

Concerns over food safety have grown after radiation from the smashed Fukushima Daiichi power plant has leaked across northern and eastern Japan since March, the world's worst nuclear crisis in 25 years.

Some local authorities are testing their rice to see if it contains too much caesium.

Rice grown in the town of Tako in Chiba prefecture, 240 km (150 miles) southwest of Fukushima, was tested this week to determine if more stringent checks are needed after the town measured high radiation in the ground, local officials said.

"The results are a relief, but we consider it as only part of the procedure to determine safety in rice consumption," said Shigetoshi Abe, a Chiba official in charge of food safety.

Tako's preliminary tests, the first to be carried out according to the farm ministry guidelines announced last Wednesday, showed its rice did not contain caesium of more than 200 becquerels per kg. ?

Still, if the rice fails further tests, Chiba will not allow rice shipments from that area.

At least 14 prefectural governments in north and east Japan, which account for more than 40 percent of the country's total rice output, said last week they would test their rice for caesium before harvest season.

Becquerels measure the ability of a substance to release radiation. Caesium-134, with a half-life of two years and caesium-137, at 30 years, could cause cancer years after exposure. Excessive levels of caesium have been found in vegetables and beef in Japan since the nuclear disaster.

Japan, which produced about 8.3 million tonnes of rice last year for food consumption, mostly eats its own produce. It imports about 770,000 tonnes a year.

Rice futures prices rose sharply this week amid radiation worries, but analysts say Japan is unlikely to step up imports.