Starting from May 11th, HKEX will implement the optimization of the Market Volatility Control Mechanism (referred to as the "Market Control Mechanism") in the first phase adjustment.

The first-stage optimization measures of HKEX this time mainly include: expanding the scope of stocks covered by the Market Control Mechanism from Hang Seng Index and Hang Seng China Enterprises Index (a total of 78 stocks) to include the constituent stocks of the Hang Seng Composite Index large cap, mid cap, and small cap indices (totaling nearly 500 stocks); and the component stocks of the three Hang Seng Composite Indexes are divided into three layers, with trigger limits set at ±10%, ±15%, and ±20% of the last fill price five minutes ago.

The Market Control Mechanism is known as the Hong Kong version of the "circuit breaker mechanism", which intervenes in market trading through preset mechanisms to mitigate significant price fluctuations when securities or futures prices experience sharp rises or falls in a short period of time.

However, unlike the circuit breaker mechanism in the U.S. stock market, HKEX's Market Control Mechanism targets individual stocks rather than indices and does not force listed companies to suspend market trading. In addition, the Market Control Mechanism will allow a "cooling-off period" in the morning and afternoon of each trading day, during which triggered stocks can only trade within a specified price range.