BEIJING, May 3 (Xinhua) -- China's customs have tightened blocking illegal grain exports triggered by international price hikes.

    As the international rice and wheat prices surge to historical highs, cases of grain smuggling are on the rise, said customs officials.

    Among eastern China's coastal ports, Hangzhou Customs stopped four such attempts and blocked nearly 7 tonnes of rice and 33 tonnes of wheat in half a month. Ningbo Customs blocked more than 130 tonnes of wheat in four recent cases.

    In March, international rice prices rose to the highest in 19 years, and wheat prices rocketed to a record peak in 28 years. At the same time, China's domestic grain prices only reported mild hikes, up 5.7 percent in January and 6 percent in February.