* CSI300 -0.9 pct; SSEC -0.4 pct; HSI -0.2 pct
* Stock index futures turn bearish
* Government mulls post-crisis regulatory framework
SHANGHAI, July 20 (Reuters) - China stocks surrendered early gains and ended Monday morning lower, weighed down by financial heavyweights, and taking a bearish lead from index futures.
After a positive start, the CSI300 index lost upward momentum and ended the morning session down 0.9 percent, at 4,112.80 points. The Shanghai Composite Index lost 0.4 percent, to 3,940.15 points.
Banking, real estate and infrastructure stocks fell, but small caps extended their rebound, with Shenzhen's ChiNext up 0.3 percent.
"It is likely that there is some profit taking after the recent solid performance of the market," said Gerry Alfonso, director at Shenwan Hongyuan Securities Co.
He added that some retail investors might have considered selling when the Shanghai Composite index approached 4,000 -- viewed by some as a key psychological resistance level.
Most of the futures contracts tracking the CSI300 index of blue chips and the CSI500 index of small caps, slumped over 4 percent on Monday morning.
But with the stock market stabilizing after its recent rout following the authorities' aggressive support measures, policymakers were considering what changes needed to be made to the regulatory framework.
Vice finance minister Zhu Guangyao said over the weekend that lessons needed to be learned, signalling his intent to focus on supervision and the development of new frameworks to make it possible to weather any future market turbulence.
On Saturday, China's central bank issued guidelines to promote, and also regulate, the development of internet finance. Internet-based peer-to-peer "fund matching" firms had played an active role in grey-market margin finance -- widely viewed as the root of China's boom and bust ride over the past year.
Hong Kong stocks were also weak on Monday.
The Hang Seng index dropped 0.2 percent, to 25,354.70 points, while the Hong Kong China Enterprises Index lost 0.9 percent, to 11,745.33.
Trading remained thin under the Shanghai-Hong Kong Stock Connect, with little of the daily quota used by midday under the cross-border investment scheme. (Reporting by Samuel Shen and Pete Sweeney; Editing by Simon Cameron-Moore)