* Shanghai stocks lower, blue-chip CSI300 index down
* Losses in Shanghai stocks led by China CSSC Holdings Ltd
* China's A-shares at 25.87 pct premium over H-shares
SHANGHAI, March 21 (Reuters) - China stocks erased early gains and ended lower on Wednesday, weighed down by start-up firms, as investors booked profits in shares of technology companies.
** At the close, the Shanghai Composite index was down 0.3 percent at 3,280.95.
** The blue-chip CSI300 index was down 0.38 percent, with its financial sector sub-index losing 0.01 percent, the consumer staples sector falling 0.77 percent and healthcare sub-index shedding 0.67 percent; the real estate index gained 0.56 percent
** The smaller Shenzhen index ended down 0.73 percent and the start-up board, ChiNext Composite index, was weaker by 1.86 percent, its worst day in five weeks.
** Around the region, MSCI's Asia ex-Japan stock index was firmer by 0.05 percent.
** At 07:00 GMT, the yuan was quoted at 6.331 per U.S. dollar, 0.06 percent firmer than the previous close of 6.3352.
** The largest percentage gainers in the main Shanghai Composite index were Guodian Nanjing Automation Co Ltd, up 10.09 percent, followed by Shenzhen Geoway Co Ltd, up 10.07 percent and Heilongjiang Interchina Water Treatment Co Ltd, up 10.04 percent.
** The largest percentage losers in the Shanghai index were China CSSC Holdings Ltd down 10.01 percent, followed by CSSC Offshore & Marine Engineering Group Co Ltd, down 9.98 percent and Shanghai Baosight Software Co Ltd , down 6.39 percent.
** About 16.84 billion shares were traded on the Shanghai exchange, roughly 94.6 percent of the market's 30-day moving average of 17.81 billion shares a day. The volume in the previous trading session was 13.99 billion.
** As of 07:01 GMT, China's A-shares were trading at a premium of 25.87 percent over the Hong Kong-listed H-shares. (Reporting by Shanghai Newsroom; Editing by Vyas Mohan)