China's top internet watchdog has ordered online search engines to limit the number of paid-for listings and to clearly label them to avoid misleading netizens.

Companies offering web search services should also review their criteria for potential advertisers, the Cyberspace Administration of China said over the weekend as it unveiled a series of new regulations.

"Many netizens complain that they cannot tell paid-for listings from free listings in search results, and some were even affected by unqualified medical information providers," an unnamed official was quoted as saying in a statement to explain the move.