Tokyo city government on Tuesday began radiation tests on samples of food bought in shops to reassure residents amid a contamination scare after a major nuclear accident in northeast Japan.

It is rare that authorities check on products at the point of sale and the the inspection includes processed food as well as fresh produce.

The metropolitan government is measuring radiation on vegetables and other fresh food to complement pre-shipment tests at places of production.

"We are conducting tests on the food residents are actually buying at supermarkets and other retail stores," an official in charge of the food monitoring said, adding some Tokyo residents had requested the tests.

The city plans to conduct tests on 20-30 items a week, he said.

"Our tests are designed to complement checks that have been conducted" by the central and local governments, the Tokyo official said.

The city will post tests results on its website every week starting Wednesday. Food items found to have radiation levels above restriction levels will be banned.

A massive tsunami triggered by a 9.0 earthquake on March 11 crippled the Fukushima Daiichi nuclear plant, which has since spewed radiation into the air, soil and sea.

Japan has temporarily banned shipments of a range of foodstuffs including beef, green vegetables, milk and dairy products, small fish, mushrooms and green tea from some areas of the country after contamination was found.