China's media regulator announced on Thursday that it will investigate 52 websites on suspicion of publishing online literature that contains pornography and violence.

The State Administration of Press, Publication, Radio, Film and Television announced the campaign as part of its ongoing campaign to clean up the Internet.

The administration said that the 52 websites include Baidu Tieba, the largest Chinese communication platform provided by the Chinese search-engine company Baidu Inc; and NetEase Blog, provided by Internet giant NetEase Inc.

A publicity officer with Baidu Inc said on Thursday that the company would not comment on the authority's decision.

The move is part of a campaign called "Cleaning the Web 2014", launched by the National Office Against Pornographic and Illegal Publications under the media authority from April to November to weed out illegal content and keep it out of the reach of children.

Other websites investigated include video-sharing website tudou.com and doc88.com, an online platform for sharing documents.

The authority said it will impose punishments on the websites if the allegations, including publishing content that has violence and pornography, are confirmed.

Many of the websites published unhealthy "fairy tales" for children, with some bearing similar names to the classic German collection Grimms' Fairy Tales. Among them was one collection called Horrifying Grimms' Fairy Tales, written by an online writer under the name of Tongshengcao.

An online forum on Horrifying Grimms' Fairy Tales at Baidu Tieba, which has run posts with complete stories, was still accessible at around 4 pm on Thursday.

But the forum was quickly closed and all the posts were deleted one hour later.

The investigation into the 52 websites followed an investigation in April into Sina Internet Information Service Co, one of China's Internet giants, which was suspended from engaging in Internet publication and audio and video dissemination for placing pornographic content online.

The authority later revoked the two licenses of Sina.com, including those for Internet publication and network distribution of audiovisual programs, and fined the company up to 5 million yuan ($800,000) for publishing as many as 20 obscene articles in its reading channel and posting four Internet audiovisual programs that spread obscene information.

Ding Junjie, a media professor at the Communication University of China, said online literature is more difficult to censor due to the large number of sources and the difficulty of obtaining evidence.

"The online platforms may never have meant to host such content. But it is their duty to supervise it," he said.

Bu Wei, director of the Research Center for Media and Children with the Chinese Academy of Social Sciences, said online service providers have obligations to protect their audiences, especially children, from unhealthy contents online, as is stated by the Convention on the Rights of the Child, an international human rights treaty.