“Tiananmen Square” was one of the world’s top trending phrases on Twitter on the 25th anniversary of the student protests there that ended in 1989 in a bloody military crackdown. As the international community remembered the day by sharing stories, tweets, photos and memories online, in mainland China, social media was silenced.

In Hong Kong’s Victoria Park, thousands of people attended a vigil marking the Tiananmen anniversary. In the special administrative region of China, people enjoy freedoms of expression unkown in mainland China. 

Tiananmen Square Vigil Victoria Park Participants mourn those who killed during the military crackdown on the pro-democracy movement at Beijing's Tiananmen Square in 1989, during a candlelight vigil in front of a backdrop showing 1989's Tiananmen Square at Hong Kong's Victoria Park June 4th, 2014. Photo: Reuters/ Bobby Yip Tiananmen Square Vigil Victoria Park Tens of thousands of people participate in a candlelight vigil at Hong Kong's Victoria Park June 4, 2014, to mark the 25th anniversary of the military crackdown of the pro-democracy movement at Beijing's Tiananmen Square in 1989. Tens of thousands of people held a candlelight vigil in Hong Kong on Wednesday to mark the bloody crackdown on pro-democracy protesters 25 years ago in Beijing's Tiananmen Square, while mainland China authorities sought to whitewash the 1989 event. Photo: Reuters/ Bobby Yip

Photos and videos of nearly 100,000 people taking part in the vigils were quickly shared across social media, becoming some of the most moving snapshots of a population trying to remember those who died and those who continue to fight for civil rights. In mainland China, however, such images will never make it to people's screens.

According to FreeWeibo.com, a live database that catalogs censored tweets, the top nine blocked items in China on Wednesday and Thursday were all related to Tiananmen. Any posts containing the phrase “Six-four” the date of the massacre, the phrase “candle” or even the word “today” were blocked from China’s version of Twitter, Weibo.

Conversation or images from any memorials from Victoria Park in Hong Kong to Taiwan’s Liberty Square were immediately removed from the social media platform.

Post blocked on Weibo A screen grab from FreeWeibo.com of a Weibo post that was blocked by Chinese censors. The user posted a photo of a newspaper covering the Victoria Park vigil in Hong Kong, commemorating the 25th anniversary of the 1989 Tiananmen Square student protests and subsequent violence. Photo: IBTimes/ FreeWeibo

“That year, that day, that man, you all forgot? Many others haven’t,” one post that was blocked read.

“You can free the imprisoned body, but you can never imprison the freedom of thought. You can shamelessly kill the angry voice, but the voice of freedom will always be with ten thousand (who) stood up with candles,” another wrote, referencing the Victoria Park memorial.

As a result of sophisticated online censorship measures, top trends on June 4 instead included a celebrity marriage, discussion over the notoriously difficult college entrance exams, and a Chinese dish called "watermelon pork."