Investors in Hong Kong can buy stocks on the Shenzhen Stock Exchange and vice-versa from today, following the official launch of the Shenzhen - Hong Kong trading link.
The link was supposed to launch at the end of last year, but was delayed due to Chinese market volatility.
Shenzhen has been promoted as a hub for technology and its stock market has been linked to the US-based Nasdaq.
As a result, foreigners will be able to trade shares in almost 900 firms.
Shenzhen is Asia's busiest exchange with monthly turnover of more than $1 trillion, according to the World Federation of Exchanges data.
China has been working on ways to open up its $6.5 trillion (£5.1 trillion) equity markets to foreign investors.
Beijing has also been pushing to have its bourses included in global index providers MSCI but their latest bid was rejected in June.
The link up between Shenzhen and Hong Kong follows the launch of theShanghai-Hong Kong Stock Connect in November 2014.
It allowed international investors to trade in 568 Shanghai-listed A shares, and 315 Hong Kong stocks.
Hong Kong has benefited from the Stock Connect scheme as mainland investors look to buy overseas assets to counter the weakening Chinese yuan currency.