In one of the more extreme examples of how tense things can get on the anniversary of the June 4th, 1989, massacre of pro-democracy protesters, even references in banking transactions mentioning the date (64) were halted in China.
Users of the hugely popular WeChat online payment app found that they couldn't transfer money values that had the number 64 in them, because it is the same number as the day in 1989 when soldiers and tanks dispersed thousands of students and other rights activists from Beijing and elsewhere in China.
Hundreds, possibly thousands were killed when the tanks rolled in on the protests, which were centred on Tiananmen Square at the city's heart, although the crackdown was city-wide.
Early casualty figures from the Chinese Red Cross put the dead at 2,600, but the Chinese government says 241 died.
In Hong Kong, tens of thousands joined a candlelight vigil to mark the event, an annual commemoration that this year has an extra importance as it is the first since the pro-democracy demonstrations late last year.
The Communist Party insists the crackdown was necessary to ensure stability and lay a solid foundation for the political and economic future of China.
Calls for justice
Every year the activist group known as the Tiananmen Mothers has repeated its calls for justice for the hundreds of victims, and for the events of June 4th to be reassessed.
In their letter this year, the mothers of the victims said the government could not complain about Japan’s failure to atone for its atrocities during the second World War, when the ruling Communist Party in China had done nothing to investigate the events of that day.
"The truth of this tragedy has to this day not been laid bare to the world, and the massacre victims, who have still not received justice, cannot rest in peace," they said in a letter run by the activist organisation, Human Rights in China.
An editorial in the Global Times, part of the Communist Party's People's Daily publishing house, said that a recent letter by a group of students in the US about the events of that day "harshly attacked the current Chinese regime, twisting the facts of 26 years ago with narratives of some overseas hostile forces".
“Chinese society has reached a consensus on not debating the 1989 incident,” the editorial said.
“Students born in the 1980s and 1990s have become the new targets of overseas hostile forces. When China is moving forward, some are trying to drag up history in an attempt to tear apart society. It’s a meaningless attempt and is unlikely to be realised.”
Since 1989, the government has begun to implement some of the freedoms that the protesters on the square had sought, such as getting rid of rules dictating where Chinese could live or work and even whom they could marry.
Strong economic growth has given millions of Chinese a say in their fates and Xi Jinping’s government is engaged in a highly public campaign to crack down on the corruption which has blighted the country and which it once denied existed.
At the same time, power in China belongs exclusively to the Communist Party and independent political activity is forbidden.
China has been tightening its control over the internet since Mr Xi took over in 2012. This week, the country’s top cyberspace regulator, Lu Wei, said that the public needed to be educated to become “good netizens”.
Trying to send “89” on WeChat also didn’t work, although sending cash by other electronic payment methods using the forbidden numbers did seem to work later in the day.