In 1989 Beijing's Tiananmen Square became the focus for large-scale protests, which were crushed by China's Communist rulers.
The events produced one of the most iconic photos of the 20th Century - a lone protester standing in front of a line of army tanks.
The events remain a highly sensitive topic in China and one of the few remaining public memorials in Hong Kong has now been removed.
What led up to the events?
In the 1980s, China was going through huge changes.
The ruling Communist Party began to allow some private companies and foreign investment.
Leader Deng Xiaoping hoped to boost the economy and raise living standards.
However, the move brought with it corruption, while at the same time raising hopes for greater political openness.
The Communist Party was divided between those urging more rapid change and hardliners wanting to maintain strict state control.
In the mid-1980s, student-led protests started.
Those taking part included people who had lived abroad and been exposed to new ideas and higher standards of living.
How did the protests grow?
In spring 1989, the protests grew, with demands for greater political freedom.
Protesters were spurred on by the death of a leading politician, Hu Yaobang, who had overseen some of the economic and political changes.
He had been pushed out of a top position in the party by political opponents two years earlier.
Tens of thousands gathered on the day of Hu's funeral, in April, calling for greater freedom of speech and less censorship.
In the following weeks, protesters gathered in Tiananmen Square, with numbers estimated to be up to one million at their largest.
The square is one of Beijing's most famous landmarks.
What was the government's response?
At first, the government took no direct action against the protesters.
Party officials disagreed on how to respond, some backing concessions, others wanting to take a harder line.
The hardliners won the debate, and in the last two weeks of May, martial law was declared in Beijing.
On 3 to 4 June, troops began to move towards Tiananmen Square, opening fire, crushing and arresting protesters to regain control of the area.
Who was Tank Man?
On 5 June, a man faced down a line of tanks heading away from the square.
He was carrying two shopping bags and was filmed walking to block the tanks from moving past.
He was pulled away by two men.
It's not known what happened to him but he's become the defining image of the protests.
How many people died in the protests?
No-one knows for sure how many people were killed.
At the end of June 1989, the Chinese government said 200 civilians and several dozen security personnel had died.
Other estimates have ranged from hundreds to many thousands.
In 2017, newly released UK documents revealed that a diplomatic cable from then British Ambassador to China, Sir Alan Donald, had said that 10,000 had died.
Do people in China know what happened?
Discussion of the events that took place in Tiananmen Square is highly sensitive in China.
Posts relating to the massacres are regularly removed from the internet, tightly controlled by the government.
So, for a younger generation who didn't live through the protests, there is little awareness about what happened.