HONG KONG — A sample of powdered tea imported from the Japanese prefecture of Chiba, just southeast of Tokyo, contained traces of radioactive cesium 137, the Hong Kong government announced late Thursday evening, but they were far below the legal maximum level.

The discovery was 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.