Two of China’s highest-profile financial liberalization projects involve Hong Kong. In 2014, it introduced the Hong Kong-Shanghai Stock Connect, which allows a total of $3.4 billion to flow between the two markets each day. In December, China doubled down and began another $3.4 billion-a-day program connecting Hong Kong to the stock market in the southern Chinese city of Shenzhen.

Because Hong Kong, a former British colony, operates outside China’s limits on cross-border money flows and has long been a capital of global finance, the programs offered many Chinese investors their first chance to invest in global stock markets.

Money can flow the other way, too. But the stock market crash in China two years ago and worries that its currency could fall in value have turned many overseas investors away from mainland stocks. Rather, the programs are drawing Chinese investors like Alex Nie, who says the mainland’s stock market lacks bargains.

Shanghai and Shenzhen shares “are overvalued,” said Mr. Nie, 37, an employee in the advertising industry in Beijing who has been buying Hong Kong stocks for the last two years and who says he is a long-term investor. “Many are not worth their prices,” he said of mainland valuations.

Many other Chinese stock investors bring a shorter-term mind-set. While private pension funds and mutual funds often steer stock markets in places like the United States, markets in China are more often swayed by amateur investors and well-heeled individuals willing to take big risks.

What China has brought to the Hong Kong stock market is “very much a herd mentality,” said Andrew Clarke, the head of trading in Hong Kong at the Mirabaud Group.