Japanese milk powder maker Meiji has recalled its baby formula after discovering radioactive caesium in the product.

Shares in the firm fell 10% in early trading in Tokyo after it said it would recall 400,000 cans of the formula.

Meiji produces the milk, which is only sold in Japan, in Saitama prefecture, north of Tokyo.

The factory's location is within 200 miles (320km) of the tsunami-hit Fukushima nuclear plant.

The recall was started after tests found up to 30.8 becquerels of caesium per kilo of Meiji Step powdered milk.

The level is below recommended limits set by the Japanese government, but Meiji has gone ahead with the recall.

Milk powder is the latest foodstuff to be affected by radioactivity in Japan after shipments of beef were banned in August and rice in September, also for caesium contamination.