Shares in property developer Kaisa (1638.HKG) fell more than 18% on Monday following the sudden weekend resignation of its chairman and an announcement Sunday from the mainland company that the Shenzhen city government had blocked the sale of four projects there, South China Morning Post reported, citing a statement filed with the Hong Kong stock exchange. Shares dropped to HK$1.72 (US$0.22) from HK$2.12 on December 16 when trading was halted after chairman Kowk Ying-shing tendered his resignation, effective from December 31.