What you need to know about the Tiananmen Square crackdown 25 years ago

China's army opened fire 25 years ago on students who had protested for political reform in Tiananmen Square, killing hundreds and cementing authoritarian rule in the world's most populous country.

Here are answers to some key questions about the protests and their aftermath.

Who were the Tiananmen square protesters?

Among the protesters in and around Tiananmen Square were students, manual labourers -- including an independent union -- newly authorised small businessmen, and white-collar personnel such as academics and journalists, even judges, policemen and Communist Party cadres.

Around 100,000 students are estimated to have taken part in Beijing, a small proportion of the more than a million total protesters.

What motivated the demonstrators?

The 1980s were a time of upheaval in China, as the ruling Communist Party's most powerful leader Deng Xiaoping introduced sweeping economic reforms to replace the Maoist command system. Academics and students began to openly demand matching changes to the authoritarian political regime.

Student protests began in April 1989 to mark the death of Hu Yaobang, a pro-reform figure who had been ousted as Party general secretary by Deng and other hardliners.

Corruption and nepotism were also major issues, with protesters calling for officials to disclose their financial assets.

City residents were worried about job stability and rampant inflation -- 26 percent by the end of 1988.

At first, few students called for the overthrow of the Communist Party, but as protests continued there were more demands for Western-style democracy and freedoms, and for Deng to resign.

How and where did they protest?

Protests in Beijing and elsewhere were largely peaceful, employing non-violent tactics such as marches, banner-waving, speeches, sit-ins and hunger strikes.

Official estimates said more than a million gathered in Tiananmen Square. Several thousand took part in a hunger strike.

More than 300 cities across China saw similar protests, according to leaked official estimates. Some turned violent, with outbreaks of rioting reported in Xian and Changsha.

How did the government crack down?

China's leadership was initially split on how to handle the protests. But the hardliners won out, and on May 20 the government imposed martial law.

Students ignored demands to leave the square and Beijing residents formed roadblocks blocking access to military vehicles.

On the evening of June 3, tanks, armoured personnel carriers and tens of thousands of troops converged on the square, using automatic weapons to shoot unarmed citizens. Similar crackdowns took place in other cities.

How many people were killed?

Estimates for the number killed in Beijing vary from several hundred to more than 1,000. China's government has never released a definitive death toll.

Beijing's then-mayor, Chen Xitong, later jailed for corruption, said some 200 civilians including 36 students had died when the "counter-revolutionary rebellion" was put down, plus several dozen soldiers. He said 6,000 security personnel were wounded, compared to 3,000 civilians.

The Tiananmen Mothers, a group representing families who lost children, have collated the names of 202 killed.

The US Embassy in Beijing estimated a death toll of "more than 1,000". The Chinese Red Cross initially reported 2,600 deaths, but later retracted the figure.

Most shootings took place on surrounding streets, rather than the square itself.

Soldiers are also estimated to have killed dozens of protesters or more in other cities, including Chengdu in the southwest.

What was the international response?

Hundreds of international reporters were in Beijing for a reconciliation visit by the Soviet Union's leader Mikhail Gorbachev, ensuring the protests were broadcast live worldwide.

US and European governments condemned the crackdown, offering students and activists asylum and briefly leaving China diplomatically isolated.

The US and EU imposed arms sales embargoes, though some European countries have continued providing Beijing with weapons.

What were the effects in China?

The US-based Dui Hua foundation estimates up to 100 people were executed and 15,000 detained. Others escaped into exile.

More liberal Communists, most notably Party general secretary Zhao Ziyang, were firmly excluded from the top leadership.

Deng pursued economic reforms while keeping tight restrictions on any political dissent, a path followed by subsequent leaders to this day, including current President Xi Jinping.

How are the protests remembered today?

China has for decades strictly censored public discussion of the crackdown, leaving a huge swathe of young people entirely ignorant of the event. Public commemorations are also strictly banned, though some Chinese activists hold private memorials.

In Hong Kong, which has robust protection of freedom of speech and assembly, an annual candlelight vigil regularly attracts more than 100,000 people, and smaller events are also held by rights groups around the world. -- AFP