The agreement, which could potentially benefit companies such as smartphone maker Xiaomi Corp <1810.HK>, relates to investments in the stock connect scheme which links exchanges on the mainland with the Hong Kong bourse.
"The three exchanges will promptly work on formulating relevant rules and will announce them to the market after completing necessary procedures," the Hong Kong stock exchange said in a statement.
The new rules were expected to be implemented in the middle of next year, it added.
The stock connect scheme allows Chinese investors their only direct means of trading offshore stocks, and international investors access to China's companies.
The agreement comes five months after the Shanghai and Shenzhen exchanges caught investors and exchange officials off guard when they said they would not allow mainland investors to buy shares in Hong Kong-listed companies with different voting right structures. - Reuters