One of the largest sources of internet giant Baidu Inc's revenue has been put under threat as a government investigation looks into the company's search business after the death of a cancer-stricken college student.

Officials from the Cyberspace Administration of China, the National Health and Family Planning Commission and the State Administration for Industry and Commerce - the regulator of online advertising, launched a joint probe on Monday after the 21-year-old Wei Zexi sought out a controversial treatment advertised among Baidu's search results.

But the procedure failed to save Wei's life. He called the treatment useless and criticized Baidu's paid listing practice in online posts before he died last month.