HONG KONG — A sample of powdered tea imported from the Japanese prefecture of Chiba, just southeast of Tokyo, had 9.3 times the legal maximum level of radioactive cesium 137 allowed in food, the Hong Kong government announced late Thursday evening. Hong Kong’s legal limits for radioactive material in food are low and stringent. But the discovery is not the first of its kind. The government’s Center for Food Safety found three samples of vegetables from Japan with “unsatisfactory” levels of radioactive contaminants in March 2011, the month that nuclear reactors in Fukushima, northeast of Tokyo, suffered partial meltdowns following a powerful earthquake and tsunami. Other samples of Japanese food have occasionally been found to have low levels of radiation since the Fukushima disaster, the Hong Kong food center said. Some tea samples were found in Japan with radioactive contamination in the months immediately after the earthquake and tsunami. Tea plants can live at least 30 years and sometimes much longer. The Hong Kong government said that it would not allow the contaminated tea to be sold and would follow up with the importer.