Note: I'm using the term skill from a manufacturer's POV as being something that can not be simply done by a machine. Whether that is R&D or creativity as part of a manufacturing process.
It is obvious they feel underpaid. It is their interest to get the most pay for their labour as they can get. Doesn't mean that the economy can afford to pay them more. Nor does it mean they would be paid more with a different unskilled job. China's struggle is that it has a massive surplus of unskilled labourers. The only way they can keep these people employed is by producing unskilled jobs for a low cost.
What is an example of an unskilled job? Sticking stickers on products. How much does it cost to get a machine to do it? $X. Then if a human wants to do it they must be to do at a comparable cost, otherwise market forces will eliminate his job. China is leaving low value manufacturing in coastal regions (where most of the manufacturing is done due to lower logistic costs). The unskilled migrant workers who haven't made their saving yet, and don't soon, are going to be far worse off in the future as they will have less earning opportunity and will be competing additional against logistic costs.
Many people fail to understand that things won't start costing more if unskilled Chinese labour would cost more. What would happen is we would start using simple machines to do the work and there would be less unskilled Chinese jobs available (leading to a slowdown of the Chinese economy). Dish washer machines are rare in restaurants in China due to the cost of labour being comparable or less than a machine.