In a detention house in south China's Guangxi Zhuang Autonomous Region, on the Vietnam border, Hai Li, 18, an illegal immigrant from Vietnam, represents her fellow townspeople as they communicate with the police.

In Vietnam, many young people want to work in China because the pay is much better, Hai says. "I earn 800 yuan a month here. Back home, I could only get 450 yuan at most."

Hai came to work at a cellphone shop in the southern Hainan Province two years ago and learnt to speak fluent Mandarin, even some Hainan dialect. She was caught by border police when returning to work after the Spring Festival vacation.

Hai and the others who came with her will be deported to Vietnam. But she says, "I will come back to China with a visa. My boss in Haikou City has promised to raise my wages."

Illegal immigrants are seized by Chinese police. [File photo]

Guangxi border police have seized 1,820 illegal immigrants, stopped 4,839 others from entering and deported 2,218 people since 2009, says a spokesman with Guangxi border police.

However, at least 10,000 illegal immigrants have come to Guangxi's Chongzuo City alone, says Mo Shaoren, deputy head of Chongzuo's human resources and social security department.

Large numbers of illegal immigrant workers from Vietnam had been found in factories and farmlands of south China cities. Most came through Guangxi's Dongxing and Pingxiang border cities, the police spokesman says.

Most local young men have gone to work in larger cities, leaving a shortfall of 30,000 farmers in normal times and 50,000 during busy seasons. Vietnamese nationals often come to fill the gaps, Mo says.

Vietnamese nationals are welcomed in Chongzuo, where they are seen as hard-working and cheap, accepting only half the wages of a Chinese worker.