3 MIN. DE LECTURA
* CSI300 -1.7 pct; SSEC -1.4 pct; HSI +0.4 pct
* Blue-chips fall after insurance investment rules tightened
* Hong Kong rises before market shuts for Christmas break
SHANGHAI, Dec 24 (Reuters) - China's stock market fell more than 1 percent on Thursday morning, as investor interest in blue-chips suddenly cooled after regulators tightened rules for insurers investing in listed firms.
The blue-chip CSI300 index fell 1.7 percent, to 3,802.61 points by lunch break, while the Shanghai Composite Index lost 1.4 percent, to 3,585.02 points.
But Hong Kong stocks ended the holiday-shortened session firmer, helped by an extended rebound in energy shares, joining Christmas cheer in global markets.
The Hang Seng Index added 0.4 percent, to 22,138.13 points, while the Hong Kong China Enterprises Index gained 0.7 percent, to 9,953.21.
Hong Kong markets closed at midday, and will be closed on Friday for Christmas.
On the mainland, blue-chips have been buoyant recently amid signs that cash-rich insurers have embarked on a year-end shopping spree as they aggressively build positions in modestly-valued big-caps - in some cases becoming listed companies' major shareholders.
But the game of betting on insurers' next acquisition target ground to a halt, after regulators issued rules late on Wednesday requiring them to make more detailed disclosures when their holdings in a listed company amount to 5 percent.
Such measures, which makes insurers' stock investments more cumbersome, hit share prices of companies investors had bet would attract more investment from them.
Retailer Dashang Co Ltd tumbled 5.9 percent, developer Gemdale Corp slumped 8.1 percent and Chinese traditional medicine maker Beijing Tongrentang tanked 7.8 percent.
"Insurers' strategy of actively expanding their stock portfolio has caught a lot of attention," brokerage Shenwan Hongyuan Securities Co said in a research note, warning investors of policy risks.
Stocks fell across the board, with property shares leading the decline.
Shenzhen's start-up board ChiNext fell nearly 1 percent, partly on concern over increased supply, after China's State Council said late Wednesday that Beijing would explore a pilot scheme allowing companies listed on over-the-counter equity exchanges to migrate to ChiNext.
Hong Kong stocks drew optimism from strength in global equity markets and a rebound in commodity prices.
An index tracking energy shares in Hong Kong jumped 2.3 percent.
Reporting by Samuel Shen and Kazunori Takada; Editing by Richard Borsuk