China's carmaker BYD Co, backed by Warren Buffet, posted a slump in first-quarter net profit compared with a year earlier, citing sluggish traditional auto business. Net profit plummeted 89.35 percent to 11.97 million yuan (about 1.91 million U.S.dollars) in the first three months, said a report on the website of the Shenzhen Stock Exchange on Saturday. During the January-March period, BYD's revenue went down by 9 percent on an annual basis to 11.7 billion yuan, it added. The Shenzhen-based company attributed the poor performance mainly to its shrinking market share in the traditional auto market, and forecast its petrol and diesel car sales to fall in the first half of the year. On the positive side, BYD saw profit grow from the sales of its all-electric bus K9 and its plug-in hybrid compact sedan called Qin. The company, which also makes mobile phone components, also benefited from a booming smartphone market in China, and sold more phone shells in the first quarter to domestic and foreign customers. BYD, which is listed in Hong Kong and Shenzhen, expects losses in its solar energy business in the first half. However, the business is starting to recover as the global solar industry rebounds from a two-year slump.