China stocks again volatile, US bond king calls Shenzhen 'short of a lifetime'
* CSI300 -0.6 pct; SSEC -0.1 pct; HSI -0.9 pct
* Shanghai index tops 5,000 level, then retreats
* Gross sees short opportunity, but 'not just yet'
* ChiNext market seeing shift to blue-chips - traders
By Samuel Shen and Pete Sweeney
SHANGHAI, June 5 (Reuters) - China stocks remained volatile on Friday, with the Shanghai benchmark shooting above a key psychological level at the opening but then shedding all gains by midday.
Shenzhen's ChiNext index, bellwether of the recent bull run, lost more over 1 percent, with investors becoming increasingly cautious about a growth market U.S. bond king Bill Gross called the "short of a lifetime".
The Shanghai Composite Index opened above 5,000 points - a key technical resistance level - but ended the morning 0.1 percent lower, at 4,941.01 points. The CSI300 index fell 0.6 percent to 5,148.95 points.
Hong Kong stocks also fell. Continuación...