The Hang Seng Index dived by 474 points, or 1.63 percent at 28,661.
Turnover was HK$91.76 billion as of noon.
Shares in Anta Sports (2020) slumped by 7 percent at HK$132.3 after the company announced that it has been informed by its controlling shareholder Anta International about a planned placement of an aggregate of 88 million shares, a 3.26 percent of the issued share capital at a price of HK$131.48 per share.
Anta was the worst performer among blue chips in the morning session.
Meanwhile, Towngas (0003) was the top gainer. Shares gained by 0.5 percent.
In the mainland, Shanghai Stock Exchange Composite Index edged up by 0.15 percent and Shenzhen Stock Exchange Composite Index also inched up by 0.22 percent.