* HSI -1.1 pct, H-shares -0.9 pct, CSI300 +0.1 pct
* Investors sell high-beta stocks amid uncertainties in Asia
* CNOOC jumps to 6-month high after positive H1 results
* Biostime rises 7.9 pct after H1 profit
By Yimou Lee
HONG KONG, Aug 21 (Reuters) - Hong Kong shares fell again on Wednesday as cautious investors sold high volatility counters on concerns over outflows from Asian markets and uncertainty over whether a coming China economic survey will be encouraging.
The Hang Seng Index, which has dropped the past four days, was down 1.1 percent at midday to 21,724.93 points, its lowest since Aug. 8. The China Enterprises Index of the top Chinese listings in Hong Kong fell 0.9 percent.
The CSI300 rose 0.1 percent, as did the Shanghai Composite Index, which was at 2,074.26 points. Both reversed early losses just before the midday break.
"Most investors are trying to reduce their risks. They are selling some high-beta stocks," said Core Pacific-Yamaichi head of research Castor Pang. "This will be the major trend for the short term."
The HSBC China "flash" manufacturing purchasing managers index (PMI) for August, the earliest indicator of manufacturing activity in the mainland, is due on Thursday.
Official media reports on Wednesday said that Beijing is planning to set up a committee system to enhance the regulation and coordination in the country's financial industry. The committee will regulate financial instruments, currency and financial policies, according to the reports.
The news came after a glitch in Everbright Securities' trading system last Friday caused its accidental purchase of more than $1 billion worth of mainland shares.
Shares of Everbright Securities, which plunged the maximum 10 percent limit in Shanghai on Tuesday, fell another 5 percent. Mid-sized Chinese banks were broadly weak, with Minsheng Bank down 0.9 percent.
China's top offshore oil explorer CNOOC Ltd jumped 4.2 percent to a six-month high after the company posted on Tuesday a better-than-expected first-half profit and said it is on track to meet its 2013 output target.
Chinese coal producer and distributor China Coal Energy Co Ltd dropped 2.1 percent reporting a 38 percent year-on-year fall in first-half net profit.
Infant formulas producer Biostime International Holdings Ltd jumped 7.9 percent to a two-month high after its first-half profit rose 8.6 percent from a year earlier. During that half, it paid a fine of 162.9 million yuan ($26.6 million) imposed by the National Development and Reform Commission for price-fixing.