HAIKOU, Aug. 9 (Xinhua) -- Police in south China's Hainan Province have detained 21 people involved in a cross-border drug trafficking ring and seized 11.7 kg of heroin, local authorities said Thursday.

Police in the city of Sanya also seized 190 grams of methamphetamine, six cars used for transporting drugs and 74,100 yuan (around 10,854 U.S. dollars) of drug money.

In an investigation that lasts a year, the police found the suspects had been transporting drugs to Hainan from overseas in large quantities.

In July, police launched raids in several cities in the province, leading to the detention.

Further investigation is underway.