By Chen Shiyin and Zhang Shidong Jan. 22 (Bloomberg) -- China's stock market has become the most expensive in Asia, leading strategists at Citigroup Inc., HSBC Holdings Plc and UBS AG to warn investors to stay away. Shares traded on mainland Chinese exchanges cost twice as much relative to earnings as they did 18 months ago, and double the average for emerging markets, after extending last year's 121 percent rally in the Shanghai and Shenzhen 300 Index. The surge sent their value above $1 trillion for the first time and prompted the government to caution shareholders that ``blind optimism'' is driving gains. continued here. http://bloomberg.com/apps/news?pid=20601087&sid=aWZ8dysagBOI&refer=home