China should gradually increase the retirement age as part of a solution to fill a possible future pension fund gap, according to a green book on population and labor released on Wednesday.

The green book, released by the Chinese Academy of Social Sciences, proposes a timetable for increasing the retirement age.

It suggested that all female employees retire at the age of 55 starting from 2018, and the age will then be increased by one year every three years until 2045, said the green book.