SHANGHAI—A rare corporate takeover fight has broken out in China, as executives at the world’s largest property developer try to thwart an unsolicited effort to take control of the company.

China Vanke Co. on Friday halted trading in its shares and said it has plans to issue an undisclosed number of new shares, without releasing details. Analysts said the announcement signals that Vanke has effectively adopted a poison pill, an antitakeover defense that can make buying up more share prohibitively expensive.

The move came after a group of three Chinese investors in recent weeks became Vanke’s largest shareholder, with a combined 22% stake. Speculation over the effort has sent Vanke shares that trade in China up by two-thirds over the past month alone, at a time when China’s property sector remains in a slump. On Friday its Chinese shares were valued at a combined 240.8 billion yuan, or about $37.1 billion.

On Thursday, Vanke Chairman Wang Shi criticized the group in front of other company executives, according to a transcript of the meeting seen by The Wall Street Journal. He singled out a Chinese businessman named Yao Zhenhua, who Mr. Wang said was behind the group, and questioned the adequacy of the financing behind the group’s share purchases.

“The reason for not being welcoming is simple: He lacks credibility,” said Mr. Wang, according to the transcript.