Officials in the Japanese prefecture of Shizuoka have asked five tea manufacturing plants to stop shipping green tea leaves after they were found to contain excessive levels of a radioactive material.

The tea leaves contained 580 to 650 becquerels of radioactive cesium per kilogram, above the legal limit of 500 becquerels. The product was tested due to fears of contamination in the aftermath of the Fukushima nuclear plant disaster.

The plant's nuclear reactors failed after its cooling systems were damaged in March 11 earthquake and tsunami, triggering radiation leaks.

Shizuoka, located more than 400 kilometers south of Fukushima, is one of Japan's leading tea-producing areas.