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.

In April, the parents of a 21-year-old student in Shaanxi province said their son had wasted valuable time in his fight against synovial sarcoma, a rare soft tissue cancer, by pursuing an ineffective treatment he had discovered on Baidu, China's biggest search engine.

Wei Zexi, who died on April 12, received four treatments at the Second Hospital of the Beijing Armed Police Corps that were meant to use cells from his immune system to kill cancerous cells. The hospital's paid-for listing came second on a Baidu search about the cancer, Wei's parents said.

The news sparked public concern over the practice of search engines allowing companies to pay to ensure their listings are placed high in search results. The internet watchdog launched a probe into Baidu and ordered the company to change its ways.

On Saturday, Baidu issued a statement saying that commercial content now accounts for no more than 30 percent of its search results.

Every paid-for listing is also now labeled, while listings for 2,518 medical institutions have been removed after a review of their qualifications, the company said. It added that it will strictly abide by the new rules.

Zhu Wei, deputy director of the China University of Political Science and Law's Communication Law Research Center, welcomed the regulations, which come into effect on Aug 1, as he believes they will make it easier to govern cyberspace.

"However, paid-for listings are not directly identified in the regulations as advertising, and how to define them is still in a legal gap," he said. In other words, search engines are not traditional advertisers covered by the Advertising Law, so any further ruling should come from a revision of that law, he added.

In addition to the rules on advertising, the regulations say search engines should provide channels for users to report bad listings to enhance public supervision.

caoyin@chinadaily.com.cn