The correct answer is - from rural to urban areas.
With the economic development that China has been experiencing in the past few decades, lot of things changed in the country. The large cities became even larger, modernized, all sorts of industries developed in them, the wages became higher, and much more opportunities for the people have been opened up. This has led to a mass migration of the Chinese workers from the rural areas to the urban areas. The rural areas did not experienced such development as the urban areas, so in order to have better living conditions and better jobs, millions of Chinese workers moved from the villages and small towns toward the large cities and megalopolises.