* CSI300 +0.1 pct; SSEC -0.1 pct; HSI -0.5 pct
* ChiNext index is up 35 pct from its mid-Sept low
* Sinosteel unit falls after interest payment delay
SHANGHAI, Oct 20 (Reuters) - China stocks ended Tuesday morning roughly flat as robust gains in tech-heavy small-caps offset weakness in cyclical stocks such as banking and real estate.
The blue-chip CSI300 index edged up 0.1 percent, to 3,536.73 points by lunch time, while the Shanghai Composite Index dipped 0.1 percent, to 3,383.75 points.
But the start-up board ChiNext rose 1.9 percent, and has now rebounded 35 percent from its mid-September low. The benchmark indexes have gained roughly 13 percent during the same period.
Hong Kong stocks retreated on Tuesday, showing signs of fatigue following three consecutive weekly gains.
The Hang Seng index dropped 0.5 percent, to 22,964.98 points, and the Hong Kong China Enterprises Index lost 0.8 percent, to 10,603.74.
China data released on Monday - including better-than-expected third-quarter economic growth of 6.9 percent - eased angst about a hard landing and offered some evidence of success in China's economic restructuring.
"Clear winners in this round of rebound are ChiNext-listed stocks. They are outperforming bluechips by a lot," said Chang Chengwei, analyst at Hengtai Futures.
However, he questioned sustainability of the rally, reasoning that ChiNext shares are already expensive and "the current economic situation doesn't justify a bull market."
Sectors including banks, real estate and infrastructure fell on Tuesday, but the main indexes were underpinned by IT, telecom and healthcare stocks.
Shares of Sinosteel Engineering & Technology Co Ltd slumped 3.3 percent, after its state parent Sinosteel said it would delay payment to bondholders.
In Hong Kong, all main sectors with the exception of telecom shares lost ground.
Among the biggest fallers were commodity-related stocks , which were hit by lingering worries about China's economic health. (Reporting by Samuel Shen and Pete Sweeney; Editing by Richard Borsuk)