South Korea's top automaker, Hyundai Motor Co., is enjoying a sharp rise in sales of midsize autos in China, which could lead to a rise in its profitability, industry sources said Sunday.Sources said that Hyundai Motor sold a total of 135,386 midsize sedans such as the YF Sonata in China last year, up 15.4% from a year earlier, according to South Korea's (Yonhap) News Agency. The YF Sonata, which was introduced in China in 2011, led the overall growth last year with a total of 104,670 units sold in the world's biggest auto market.In particular, the carmaker's newly released sedan, the Mistra, is showing signs of becoming the South Korean automaker's another best-selling product in the neighboring country.Hyundai has sold 16,762 Mistras in China since its market debut in November last year. In December alone, the automaker sold 10,502 units, the source said.Hyundai Motor unveiled the Mistra, exclusively tailored for China, expecting to sell 100,000 of them this year as it seeks to tap China's growing middle class. The carmaker's profitability is expected to improve as well, with the portion of its middle- and large-size sedans and sport utility vehicles to total sales in the neighboring country rising to 40.7% last year from 33.75 a year earlier, according to the sources. Hyundai Motor and its smaller affiliate Kia Motors Corp. sold a combined 1.57 million units in China last year, up 18% from 1.22 million units a year earlier.Beijing Hyundai Motor Co., a joint venture between Hyundai and Beijing Automotive, operates three assembly plants in Beijing, where it is set to finish the ongoing expansion of one of the plants this year. Hyundai will have an annual production capacity of 1.05 million units when the expansion is completed.