The government-linked Internet Society of China plans to compose "self-discipline standards" for microblogging services, a group representative said in an e-mail. The representative declined to give details, but the group has released similar guidelines for other Web sites before. A document the group released for blog providers calls for them to delete "illegal or harmful information" as it appears on their sites, or simply to cease blog service for infringing users. Chinese authorities have used the term "harmful information" to describe online content including pornography and discussion of politically sensitive topics such as Falun Gong, a spiritual group banned in the country.

Twitter and Facebook have been blocked in all of China since July, when deadly ethnic riots in the country's western Xinjiang region led it to crack down on communication tools that could be used to gather people at a given location. Authorities also blocked all Internet service and text messaging in Xinjiang after the rioting, which state-run media say killed nearly 200 people.

Some Chinese-language Twitter rivals also went offline after the rioting. One of the bigger sites, Digu, came online again last month, but rival service Fanfou is still down.

Chinese authorities already appear to have pressured local microblogging sites over sensitive user messages. The services are expected to control their content themselves, said Alex Mou, CEO of local microblog site Zuosa, in a phone interview. Zuosa, which deletes sensitive posts by users, has not had major downtime in recent months because it has not drawn attention to itself, said Mou. Government authorities in contact with Zuosa have given the company reference documents about information management on the Internet, he said.

"I think in China microblogging still has strong prospects," said Mou. "Of course you have to handle some things according to China's special situation. ... Probably whoever can most effectively manage this kind of information will grow the best," said Mou.

Plurk, a microblogging service popular in Taiwan and other parts of Asia, was also blocked in China after the Xinjiang riots. That and earlier service cuts have made it more difficult to build a user base in China, said Alvin Woon, a co-founder of Plurk, in an interview.

"In order to do China, you have to be pragmatic when it comes to issues like free speech," Woon said.