SHANGHAI, Dec 23 (Reuters) - China's blue-chip index CSI300 broke a four-day rising streak on Wednesday, as a late afternoon slump in start-up board ChiNext soured market sentiment.
The CSI300 index surrendered earlier gains, dipping 0.3 percent, to 3,866.38, while the Shanghai Composite Index lost 0.4 percent, to 3,636.09 points.
Tech-heavy ChiNext tumbled 2.2 percent, as selling intensified toward the market close.
Sentiment was initially upbeat amid fresh signs that cash-rich insurers were on a shopping spree at the year-end, buying modestly-valued big caps.
But the late-afternoon sell-off reminded investors of the liquidity pressure from five companies that start taking subscriptions on Wednesday for their initial public offerings.
Some traders say the rally in blue-chips is still sustainable, although small-caps could weaken further.
"Insurers' purchases have put blue chips into the market's spot light," said David Dai, Shanghai-based investor director at Nanhai Fund Management Co.
He added that small-caps were more expensive and thus faced heavier selling pressure as a six-month share sale ban by major shareholders expires in early January.
Latest exchange filings showed that insurers have been boosting stakes in blue chips, including developer China Vanke Co , retailer Chang Chun Eurasia Group and Chinese traditional medicine maker Beijing Tongrentang Co.
Highlighting insurers' intensified purchase activity, the official China Securities Journal estimated that in December alone, median-sized insurer Anbang Insurance Group had spent more than 30 billion yuan ($4.63 billion) buying stocks.
$1 = 6.4752 Chinese yuan Reporting by Samuel Shen and Nathaniel Taplin; Editing by Jacqueline Wong