Chinese police blocked the gate of a cemetery housing victims of the Tiananmen crackdown on its 24th anniversary on Tuesday, part of a sweeping annual effort to bar commemorations of the event.
Authorities launch a major push every June 4 to prevent discussion of the violently crushed 1989 pro-democracy protests, China's darkest human rights stain in recent decades, in which at least hundreds of people died.
More than a dozen security officials deployed outside the stone gate at the Wanan graveyard near the hills of western Beijing, which mothers of the victims visit each year, and told AFP journalists to leave the area.
Authorities also detained or enhanced surveillance of 10 prominent dissidents, according to the Hong Kong-based advocacy group China Human Rights Defenders.
Online searches for a wide range of keywords on Sina Weibo, China's version of Twitter, were blocked, from "Tiananmen" to "candle", which was used to encourage digital vigils.
Activists turned instead to overseas websites to commemorate the event and criticise authorities.
"The dispute in this country is basically stuck on whether to light a candle or to extinguish it," dissident artist Ai Weiwei posted on Twitter.
Rights lawyer Liu Xiaoyuan said on Twitter that he had been blocked from Sina Weibo for seven days for sharing "sensitive information" -- urging others to honour victims by posting an image of a lit candle.
A mocked-up picture was circulating online of the 1989 "Tank Man" photograph of a civilian staring down a long row of tanks headed toward Tiananmen Square -- with the military vehicles replaced by plastic ducks.
The image could not be found on domestic websites within the "Great Firewall of China", as the country's system of Internet controls is known.
The high-profile dissident Hu Jia wrote on Twitter that the broad crackdown on discussion of Tiananmen demonstrated the government's weakness.
The event underscored the ruling Communist Party's "illegal nature", he wrote. "The unprecedentedly high pressure for the 24th anniversary of June 4 actually reveals the authorities' fear."