A PhD dissertation written by President Xi Jinping 13 years ago, in which he urged reform of the hukou, or household registration system, was made public on Wednesday.

The system has created a large income gap between rural and urban residents that should be corrected in a prudent and proactive manner, Xi wrote.

The dissertation, part of a library collection at Tsinghua University, was written in December 2001 when Xi, then governor of East China's Fujian province, was studying economics at Tsinghua for a doctoral degree.