China's Ministry of Public Security is considering a permanent number for Hong Kong and Macao residents' mainland entry cards for convenience.

Currently, the last two of the 11 digits indicate the frequency for card renewals, meaning the number changes when Hong Kong and Macao residents get their cards renewed. That has been an inconvenience for those investing, buying housing, and doing banking business on the mainland.

According to a statement released Friday by the ministry, Hong Kong and Macao residents entered a peak period for mainland card renewals last year.

Cards for those aged 18 and above are valid for ten years. Cards for those under 18 years last three years.

The mainland entry cards began to be used on Jan. 15, 1999.