Stock Connect and Quota-Based Market Access

Before 2014, buying mainland Chinese A-shares as a foreign investor required a special quota-based license (QFII) that was slow and capped in size. Stock Connect changed that by linking the Hong Kong exchange directly to the Shanghai and Shenzhen exchanges, letting international investors buy eligible A-shares through an ordinary Hong Kong brokerage account, and letting mainland Chinese investors buy eligible Hong Kong stocks the same way, in both directions ("Northbound" and "Southbound" flow).

Access isn't unlimited. Each side of the link has a daily net-buy quota, and if aggregate buying hits the ceiling, new buy orders stop until the next trading day resets it. In practice the daily quota is rarely binding for the whole market, but it can bind hard for a single popular stock during a burst of buying, effectively freezing new foreign demand for that name mid-session.

Worked example

Ahead of an A-share index-inclusion event, global index funds all try to buy the same newly added stocks on the same day through Northbound Connect. If aggregate Northbound buying interest that day approaches the daily quota, HKEX suspends new buy orders through the link once the ceiling is hit, forcing funds that didn't get filled to try again the next trading day — a mechanical constraint that has nothing to do with the stock's price or fundamentals.