More than six times the legal limit of radioactive caesium has been found in beef from Fukushima prefecture, home to Japan's crippled nuclear plant, an official statement said on Saturday.

The meat was taken from one of 11 cows shipped to Tokyo from a farmer in Minamisoma city, according to the statement by the Tokyo metropolitan government.

The 11 cows all showed high levels of radioactive caesium, ranging from 1,530 to 3,200 becquerels per kilogram, compared with the legal limit of 500 becquerels, the Tokyo statement said.

It was the first time excessive levels of radioactive caesium have been found in meat, according to a Tokyo official.

"All the meat from the cows is kept in the laboratory and has not entered the market," a separate statement said.

The city of Minamisoma lies on the outskirts of the Fukushima Daiichi nuclear power plant, which has leaked radioactive substances into the environment after the March 11 tsunami and earthquake crippled its cooling systems.

The 11 cows were raised and shipped by a single farmer in the city's district just outside of the 20-kilometre no-go zone around the plant, the statement said.

- AFP