As a manufacturing base, China holds strong appeal for Detroit’s automakers. Auto factory pay in China is similar or slightly higher than in Mexico at around $1,250 a month, including government-mandated benefits like contributions to savings funds with which workers can buy housing. Overtime adds roughly $300 a month. But that pay is much lower than in the United States, where workers earn several times as much even before overtime.

Auto parts are also much cheaper in China than in the United States, because labor tends to be a larger share of the cost than final assembly. The global auto parts industry has shifted much of its production to China, partly because of low costs and partly because China’s steep tariffs make it impossible for multinational manufacturers to compete in the Chinese market unless they produce in China.

And quality is high at Chinese factories run by Western carmakers.

Global automakers already have built some of their most modern factories in China. A Ford factory in Hangzhou has 650 robots. A somewhat smaller General Motors factory in Shanghai has 530 robots that make Cadillacs with all-aluminum bodies — one of the latest and toughest manufacturing challenges even in the West.

G.M.’s China-made Buick Envision ranks slightly above average in initial quality surveys of American consumers among 13 compact sport utility vehicles, according to J.D. Power and Associates, the international quality rating company. The top three concerns of the Envision’s American buyers involved the ease of use of its voice recognition system and other consumer electronics — concerns indicating that American consumers were basically satisfied with the actual car.

Chinese domestic automakers still lag in quality surveys. But among the global brands, cars made in China come from assembly lines that are identical in almost every respect to factories in the West — except that the factories in China, because they are new, tend to be more automated. Jeff Cai, the general manager of the China automotive practice at J.D. Power, said that the relative newness of Chinese factories tended to balance out the limited experience and high turnover of Chinese workers.

“In terms of the building quality,” he said, “it’s pretty similar.”

Industry insiders fear that all the auto factory capacity will encourage China to increase exports if homegrown demand slows down. Thanks to a cut in sales taxes last year, car sales in China in 2016 grew by an amount almost equal to the entire Japanese market. That helped absorb some of China’s overcapacity. But with the partial expiration early this year of the sales tax cut, demand is starting to slow.

Ford’s sales in China in the first five months of this year were down 11 percent from the same period last year. But Sinead Phipps, a Ford spokeswoman, denied any connection to the new export plans. “We’ve made the decision because it allows us to reduce global Focus production by one plant, improve the health of our Focus business, save $1 billion in investment costs and further improve our scale in China,” she said.