NANNING, Feb. 12 (Xinhua) -- A total of 36 Vietnamese nationals who attempted to enter China without official documentation were repatriated by Chinese police on Wednesday, local authorities said Thursday.

The suspects had been held in Dongxing City, in south China's Guangxi Zhuang Autonomous Region. Dongxing is located on the China-Vietnam border and is adjacent to the Vietnamese city of Mong Cai.

According to local police, criminal gangs, known as "snake heads", recruit people from Vietnam with the promise of high paying jobs in Hong Kong, they are told they must travel overland to Hong Kong.

Guangxi police had uncovered 145 illegal immigrant cases in its two-year campaign, and apprehended 233 suspects, local authorities said in January.

The illegal migration of people across Chinese borders has increased in recent years, with snake heads charging exorbitant "transportation fees" for unregistered drivers and tour guides, said Li Yue, deputy head of the regional public security department.