BEIJING—A senior Chinese official said in 2007 that much of the country's local economic data are unreliable, according to a leaked diplomatic cable published by the WikiLeaks website.

The official, Li Keqiang, was at the time Communist Party secretary of the northeastern province of Liaoning, and has since been promoted to vice premier. Since landing that position, he has overseen many of the central government's efforts to improve the quality of its economic statistics, which continue to face many questions over their accuracy...