Authorities have launched a crackdown against the spreading of rumors and other harmful content through instant messaging services such as WeChat.

The crackdown was launched on Tuesday by the State Internet Information Office, the Ministry of Industry and Information Technology and the Ministry of Public Security.

It targets the spreading of rumors and other information harmful to national security and the public interest through public accounts and chat groups on instant messaging platforms, the office said in a statement.

WeChat, designed by Internet giant Tencent, is a popular mobile text and voice-messaging app in China with 650 million individually registered accounts.

The number of WeChat public accounts, which deliver customized information to an unlimited number of followers, had reached 3 million, the office said.

An official at the office, who did not want to be identified, said the large number of public accounts and various chat groups, which allow up to 500 participants, had become a channel for the spreading of rumors and other harmful content.

The official said the campaign would focus on key targets including the spreading of malicious content like violence, terrorism and pornography through public accounts.

A joint statement issued by companies behind the messaging services, including Tencent, said they would increase the scrutiny of public accounts in line with the latest crackdown, including measures that examine public accounts and shut those that spread rumors.

Last month, a Beijing court sentenced Internet rumormonger Qin Zhihui, known online as "Qinhuohuo", to three years in prison for defaming celebrities and the government.

The authorities will also introduce more measures to encourage the use of government WeChat accounts to address public concerns. Mainstream media and news portals will also be encouraged to use WeChat or other platforms to increase their visibility and reach.

Hou E, a senior researcher at the Institute of Public Relations at Communication University of China who studies new media, said challenges remained for government WeChat accounts to increase their popularity among users.

"Our research showed that some government WeChat account feeds are rarely opened by users. Authorities should provide users with more attractive feeds."

Zheng Yi, operations manager of Momo, an instant messaging app, said the company had taken measures requiring users to register for its service with their cellphone numbers to increase scrutiny of their accounts.