Top Chinese social networking sites offering services similar to Twitter have experienced sporadic service disruption in recent days, triggering fears that a government crackdown could be on the way.
Netease.com's service was inaccessible on Wednesday, bearing a notice that said it had been under "maintenance" since the previous evening.
Sohu.com also has confirmed its service was shut down for three days from last Friday, the Beijing Evening News reported.
Sohu's service appeared to be operating normally on Wednesday, as did those of other major Chinese portals such as Tencent.com and Sohu.com.
The mysterious problems have triggered speculation in Chinese Internet chatrooms and on the services themselves that a crackdown by government censors could be imminent.
Adding to the speculation is the sudden addition of the words "beta" or "test version" seen on the homepages of some of the services, which some users said indicated the government may impose demands on future versions.
China, which has more than 400 million web users, operates an extensive system of Internet censorship dubbed the "Great Firewall of China" that is aimed at filtering out any information deemed sensitive or politically harmful.
Blocked foreign-based Internet sites include Youtube, Facebook and, since last year, Twitter.
A number of Chinese versions of Twitter have emerged to fill the void and have become increasing popular with users.
But Shanghai's Oriental Morning Post on Wednesday quoted an "industry official" saying currently no specific policies govern micro-blogging, apparently hinting that some could be in the offing.
"As long as the policy is ambiguous, micro-blogging will continue to face a severe test," the official was quoted saying.
Various state press reports quoted representatives of major micro-blogging providers as denying the recent problems were due to government interference, saying they were routine maintenance issues.
Representatives of Sina.com, Sohu.com, and other major providers could not immediately be reached by AFP.
Comments on the issue by users of social-networking sites ranged from resignation to indignance.
"What kind of government is so afraid of letting its people speak? Only one in which those in power are not considered legitimate," said a message by a user of Sina.com's micro-blogging service.Reuse content