BY YVONNE LEE AND PRUDENCE HO

HONG KONG—Haitong Securities Co. has increased the number of shares it will sell through a Hong Kong listing, boosting the potential size of its initial public offering to US$1.77 billion from around US$1.5 billion, a sign that companies are seeking to capitalize on stronger stock markets.

Haitong is the second Chinese brokerage firm to seek a Hong Kong listing; Citic Securities Co. had a US$1.7 billion IPO in October. If the Haitong deal goes through, it would be the biggest IPO this year. The current leader is a US$1.22 billion offering by the Dutch cable network Ziggo …