It is one of the most iconic photographs of the 20th century: an unidentified man stopping the advance of a convoy of tanks through Tiananmen Square.

Key points: Yesterday was the 30th anniversary of the Tiananmen Square massacre

Yesterday was the 30th anniversary of the Tiananmen Square massacre In 1989, the Chinese military broke up student demonstrations in the square

In 1989, the Chinese military broke up student demonstrations in the square China strictly censors public discussion of the protests and the subsequent massacre

"Tank man" only stared down the Chinese military briefly, but he entered the history books as a universal symbol of peaceful resistance.

Thirty years after the government's crackdown on students who filled the square demanding democratic reform, many young students today have never seen the photo.

Those who have seen it are reluctant to discuss it in public.

In 1989, the main student district in Beijing's north-west, Haidian, was a hotbed of political action.

But today's students have grown up under a government that refuses to teach the history of the Tiananmen Square uprising — referred to in China as "June 4th".

The photo of a man in front of a convoy of tanks became the defining image of the Tiananmen crackdown. ( Reuters )

The government strictly censors public discussion of Tiananmen and goes to great lengths to scrub references to it from the internet.

"I think I only have a vague impression of what June 4th is about. It's rarely talked about in China and I didn't learn it in history textbooks," said a 24-year-old journalism student who wanted to be called Lily.

"I have no idea what the event was like, or what happened exactly. I only know that maybe the Chinese government did something horrible to the protesters, I think June 4th is about that, right?"

Sorry, this video has expired Tanks in Tiananmen Square in 1989

Like many students the ABC spoke to in Beijing, Lily was not sure if she had ever seen the famous "tank man" image.

"I've heard of it but haven't seen it. Is that the guy standing in front of a tank? Maybe I saw a picture of it once," she said.

One management student from Beijing's Renmin University could not identify the tank man photo when shown by the ABC, but wondered if she had seen "similar images".

Some others said they were not aware of what the "June 4th" anniversary means.

The history of the Tiananmen protests is not taught in Chinese schools. ( Reuters: Bobby Yip )

"I've never heard of that, was it some sort of student movement?" asked a 19-year-old accounting student, who said she doesn't use VPN software to access censored websites like Google.

Even among friends, there are big differences.

How the 1989 uprising unfolded: April 15: Former Communist Party chief Hu Yaobang, a leading reformist, dies aged 73

Former Communist Party chief Hu Yaobang, a leading reformist, dies aged 73 April 18: Thousands of students march to Tiananmen Square, calling for democratic reforms

Thousands of students march to Tiananmen Square, calling for democratic reforms May 19: An estimated 1.2 million people attend a rally in Tiananmen Square

An estimated 1.2 million people attend a rally in Tiananmen Square June 4: Chinese troops retake Tiananmen Square, firing on on civilians and students

Chinese troops retake Tiananmen Square, firing on on civilians and students June 5: An unidentified man blocks a convoy of tanks before being pulled away by onlookers

Three accounting students from China's University of Mining and Technology had very different reactions when asked about the 30th anniversary by the ABC.

One of them said he genuinely had no idea about it.

His 19-year-old classmate claimed he did not know but appeared nervous when asked.

The third, a 20-year-old student, was comparatively well-informed.

"If you are a young person here who is interested in what happened, you can find ways to read about it online," he said.

But the student said he believes the government's actions in 1989 were "correct".

"Those students were very young, very easy to be manipulated. Maybe they were trying to do something, but it then morphed into something else," he said.

"What they wanted for their country is different to what I want for my country."

How China scrubbed 'tank man' from the internet

Textbooks do not mention the violence that left hundreds, maybe thousands, of students dead near Tiananmen Square.

The Chinese internet has been scrubbed of all but the official accounts.

Photos of the protests do not exist on the Chinese internet. ( Reuters: Dominic Dudouble )

Putting "June 4th" into China's biggest search engine Baidu does not bring up an error page, but rather a string of articles from state media referring to the "June 4th political turmoil".

The top result is a 2001 article from the Communist Party's official paper People's Daily, which gives a succinct one-paragraph description of what happened.

It blames a small number of "liberal intellectuals" for taking advantage of well-intentioned students to oppose the party and the socialist system.

An image search does not bring up a single photo from the protests, nor are there any results on China's largest public social media platform Weibo — aside from a few user comments.

In 2013, a Weibo user managed to briefly evade Chinese censors by turning the tank man image into a meme by replacing the tanks with rubber ducks.

This image went viral in China on social media platform Weibo on the 24th anniversary of Tiananmen. ( Weibo )

June 4 is the busiest day of the year for online censors, who block search terms including "today", "anniversary", "remember", "tank man" and "candlelight".

"Big yellow duck" was added to the blacklist when the government came across the meme in 2013.

Whatever students in Beijing know about the historic events of 1989, they mostly know to steer clear of discussing it, particularly with Western journalists.

"I've seen the 'tank man' picture. I can't remember how I viewed it. It was many years ago," said a 22-year-old law student in Beijing.

What happened to 'tank man'? The identify and fate of the man who blocked the Chinese tanks is unknown

The identify and fate of the man who blocked the Chinese tanks is unknown Some speculate he may have been a 19-year-old student who was later executed

Some speculate he may have been a 19-year-old student who was later executed But Communist Party former general secretary Jiang Zemin said he was never found

The student said he does not use VPN software to get around Chinese censorship, because it is illegal.

"I don't know what my friends and fellow students know about 1989. Everyone's different and I don't talk about this with them very much," he said.

Another student studying at Renmin University was nervous when asked about the anniversary.

"This is a sensitive topic. It's not good for us and our prospects to discuss it. The political environment here is getting tighter and tighter," she said.

Some of the students who spoke to the ABC understood why the government wanted to forget what happened in Tiananmen Square in 1989.

"Western media is maybe trying to criticise China, trying to dig out something bad the government did," Lily said.

"I can understand why the Chinese government is trying to build a positive image of China."

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