As a part of traditional planned economy, population migration and labor mobility in China were strictly controlled by the authorities before the 1980s. To be more precise, cross-regional migration was controlled by public security departments and it was almost impossible to make any rural-urban migration without authoritative plans or official agreement; Industrial transfer of labor force was controlled by departments of labor and personnel management, and there was no free labor market at all. But the most strictly controlled were the transfer from rural to urban areas, and from farmers to non-agricultural workers. This control has functioned through the Household Registration System (Hukou System), a typical Chinese registration system of permanent residence that segregates rural and urban areas strictly.
URL : http://www.rrojasdatabank.info/migration/China_invisible_hand_visible_feet.pdf