With checkpoints at entrances to the square and sentries at train stations, the security presence in and around China's symbolic political heart appeared no more overt than usual.
  
But in line with the unspoken policy of "wai song, nei jin" - relaxed on the outside, vigilant internally - plainclothes policemen mingled with sightseers following their guides, ready to pounce should one attempt to unfurl a protest banner, kneel to pray or lay a wreath.

The security ritual has occurred every year since June 4, 1989. That was when troops backed by tanks shot their way from the city outskirts to the edge of the square to end rallies for democracy that students had led there since mid-April when they had gathered to mourn the death of Hu Yaobang, a reformist leader.
  
By contrast, in Hong Kong tens of thousands of people turned out to hold a candlelight vigil to remember the hundreds, perhaps thousands, who were killed.

Police presence
 
In the square on Sunday, students appeared more interested in the sights - Mao Zedong's mausoleum, the Great Hall of the People and the history museum flank the immense open space - than in politics.

Anniversaries or the deaths of popular leaders in China have often provided excuses for protest.

There was no special police presence on Fuqiang Hutong, where Zhao Ziyang - the party secretary toppled in 1989 for sympathising with the student protesters - lived under house arrest for 15 years until his death in January last year.

"The people will not forget. Long live democracy!"

Demonstrators in Hong Kong

People walking into the alley towards the door of his home got little more than a hard stare from men in plain clothes. Still, dissidents had been rounded up before.
  
Seventeen years ago, students huddled around the Monument to People's Heroes in the middle of Tiananmen Square, waiting for the military assault. It was cordoned off on Sunday.

Subversive
  
Before the anniversary, the "Tiananmen Mothers", relatives of victims of the crackdown, called on the government to reassess the demonstrations, which it has branded subversive.

In April, authorities made a payment to the mother of one of those killed, the first case of compensation. But Ding Zilin, a retired professor whose son died in the crackdown, said she doubted that it meant any change of official policy.
   
While no big protests were reported in China proper, in Hong Kong organisers of the evening vigil said 44,000 people showed up to sing and light candles in memory of the victims of the massacre. Police said the turnout was about 19,000.
  
"Reverse the verdict on June 4th. The people will not forget. Long live democracy," chanted the crowd. In the wake of the crackdown, the government proclaimed the protests a "counter-revolutionary rebellion".