General Motors' Buick Regal
A customer looks at a Buick Regal car at a General Motors auto dealership in Shanghai Dec. 4, 2009. Reuters / Aly Song

General Motors Company's (NYSE:GM) car sales in China have slightly surpassed its U.S. sales during the first six months of 2013, a significant milestone.

The most populous nation in the world is now GM's most high-volume market. GM China's sales surged by 10.6 percent from January to June to top 1.6 million while reaching just above 1.4 million stateside.

Buick, for example, has struggled domestically yet is much more popular in China. Sales increased for Buick's Verano sedan and Excelle Xt hatchback models.

Cadillac, which currently has about 200 dealerships in China, expects to sell 50,000 vehicles in China in 2013, up from 30,000 in 2012. In fact, GM China expects to sell two-thirds more of its Cadillac brands such as the new XTS sedan during the second half of 2013 than it sold in the first half. Cadillac also expects its annual sales total in 2016 will be twice as much as 2012's total, according to Bob Ferguson, vice president of the Cadillac brand.

GM China, the republic's second-largest auto manufacturer, forecasts Chinese demand for its passenger vehicles and commercial models will remain robust through the end of 2013.

"We have seen strong vehicle demand across China, particularly in the midsize, upper-medium, luxury and SUV segments," Bob Socia, president of GM China, said. Socia said demand in June was also up 10.6 percent from last year's 236,207-unit high.

The automaker, which underwent bankruptcy in 2009, has 12 joint venture projects in China. GM China's sales outpaced Volkswagen AG's (ADR) (OTCMKTS:VLKAY) China sales, as well as Ford Motor Company's (NYSE:F) China sales. Ford enjoyed a 47 percent sales increase in 2013 and will launch six new vehicles in China this year and debut its Lincoln brand in China next year.