BEIJING - China has asked major Internet companies to strengthen their self-discipline and examination against pornographic, obscene and vulgar content online.

A total of 16 companies, including Baidu, Alibaba and Tencent, were called up by the National Office Against Pornographic and Illegal Publications recently to underscore the issue.

Based on the ongoing national campaign to clean up the online environment, including inappropriate online videos distorting popular cartoon characters and online games, Internet companies should improve their censorship of online content and the filtering of harmful information, according to the office.

The companies should not only clear the already found harmful information, but also take action to examine and eliminate its variations, in order to take on their legal duties and social responsibilities as enterprises, the office said.

Enterprises that caused harmful information to spread will face severe punishment, the office continued.

China's authorities have already handled a number of cases involving obscene content in online games and live streaming platforms this year.

One that drew much attention from the public involved two offices of the Guangzhou Yinjun Trade Company in south China's Guangdong province, which were closed in late January for producing online videos featuring popular children's characters in sexual, violent, and terrorist scenarios.