Chinese search giant Baidu Inc announced Monday that it has begun to assist police in an investigation into its promotion of gambling websites that used fake business licenses.

A slew of gambling sites photoshopped other companies' business licenses in order to register for Baidu promotional services, The Beijing News reported Monday.

According to the report, search queries with key words like "casino" entered on Baidu between 10 pm and 9 am yielded results lists topped by these sites, accompanied by the tag "Baidu Promotion."

Moreover, ends of quarters and weekends always saw a surge in both the number of such websites listed and in higher rankings for such sites.

For example, gambling and entertainment services website "The Venetian Macao" ranked near the top of the search results on Sunday and consequently saw bets increase from 79 million yuan ($12 million) to 100 million yuan within half an hour and a hike in the number of gamblers to 620,000.

All of the gambling websites were found to have later secretly modified the company information listed on the business licenses used to obtain initial promotional approval, according to a statement released by Baidu on its official Sina Weibo account on Monday.

The statement added that the company has firmly banned commercial promotion of gambling.

Liu Ming (pseudonym), a salesman working for a Baidu Promotions agency, told The Beijing News that in order to meet sales goals, some agencies give salespeople 80 percent of promotion fees as perks. The promotion fees of those websites can reach as much as 300,000 yuan per night.

Li Sheng (pseudonym), a senior salesman, said the websites' business licenses were usually faked by misappropriating other companies' information to get Baidu's approval.

According to The Beijing News, the companies whose information was forged are completely unrelated to gambling and were not registered for promotion on Baidu.