TURIN, Italy -- Chinese automaker Beijing Automotive Industry Holding Corp. will unveil the C80K concept at the Beijing auto show on Monday.The sedan hints at a potential competitor to the long-wheelbase versions of the Audi A6, BMW 5 series and Mercedes-Benz E class, which dominate China's luxury segment.The concept was designed by the design and engineering companies Fioravanti, of Italy, and Eastone, of Shanghai.The sedan, which would become BAIC's flagship if built, is 5203 mm long and 1915 mm wide.The concept is distinctive for its lack of a B-pillar and its rear-hinged suicide doors, a feature now offered only on Rolls-Royce models.Luxury cars are the fastest growing segment in China, with sales up nearly 37 percent to 130,416 units from January to March, according to Morgan Stanley in London.By contrast, the overall Chinese market was flat at 3.15 million units in the first quarter.BAIC, of Beijing, has joint ventures with Daimler AG to build Mercedes-Benz passenger cars and trucks and with Hyundai to build cars and SUVs.