Chinese authorities are seeking to block commemorations of the 24th anniversary of the June 4, 1989 crushing of pro-democracy protests in Beijing's Tiananmen Square.
There was no significant increase in the numbers of uniformed police on Tiananmen Square itself on June 4, but police blocked off a cemetery where victims of the crackdown are buried.
Activists said online searches for a wide range of keywords on Sina Weibo, the Chinese microblogging and social-networking site, were blocked in an apparent attempt to prevent discussion of the events.
In Hong Kong, tens of thousands of people were expected to attend a candlelight vigil later on June 4 to mark the anniversary.
Hundreds, and possibly thousands of people are believed to have been killed on June 4, 1989 when the military brutally ended weeks of pro-democracy protests on Tiananmen Square.
Based on reporting by AFP and AP