There are over a million legal immigrants in China, plus an unknown but sizable number of illegal immigrants, mostly from Vietnam and Myanmar. Of course this is not a huge number compared to the overall population, but it's still a sizable number of people.
They still have enough unskilled labor they can pull from the country side. They pack up the village and ship them (relocate the people) to a city in need of workers.
Lol a million immigrants, that's the net inflows the U.K is getting a year with a 60 something million population.