SHANGHAI, Dec 24 (Reuters) - China's stock market posted its biggest one-day fall in two weeks on Thursday, as investor interest in blue chips suddenly cooled after regulators tightened rules for insurers investing in listed firms.
The blue-chip CSI300 index fell 1.0 percent, to 3,829.40, while the Shanghai Composite Index lost 0.6 percent, to 3,612.49 points. Both indexes had the worst day since Dec. 8.
Blue chips have been buoyant recently amid signs that cash-rich insurers were on a year-end shopping spree as they aggressively built positions in modestly-valued big caps - in some cases becoming listed firms' major shareholders.
But the game of betting on insurers' next acquisition targets ground to a halt after regulators issued rules late on Wednesday demanding more detailed disclosures when their holdings in a listed company amount to 5 percent.
Such measures, which make insurers' stock investments more cumbersome, hit the shares of companies investors had bet would attract more investment from them.
Retailer Dashang Co Ltd tumbled 7.6 percent, developer Gemdale Corp slumped 9 percent and Chinese traditional medicine maker Beijing Tongrentang tanked 6.9 percent.
Most sectors fell, with property shares leading the decline. (Reporting by Samuel Shen and Kazunori Takada; Editing by Jacqueline Wong)