Hong Kong’s stock market extended gains into a sixth day Thursday, but trading was volatile, as investors rushed to snap up cheap shares of mainland Chinese companies.

The Hang Seng Index rose as much as 6.4%, pared gains to 1.8%, and then rebounded as the market paused for lunch, closing the day up 2.7%. The Hang Seng China Enterprises Index, a gauge of Hong Kong-listed mainland Chinese companies, rose as much as 7.3% before paring gains to 2.6%.

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