BEIJING - In Tiananmen Square, police were ready to pounce at the first sign of protest. In Hong Kong, a sea of candles flickered in the hands of tens of thousands who vented grief and anger.

Two starkly contrasting faces of China were on display yesterday, the 20th anniversary of the military's bloody crackdown on pro-democracy demonstrators - from Beijing's rigid control in suppressing any dissent, to freewheeling Hong Kong, which enjoys freedoms all but absent on the mainland.

Tiananmen Square was blanketed by security officers who were ready to silence any demonstration, and there were few hints that the vast plaza was the epicenter of a student-led movement that was crushed on June 3-4, 1989, shocking the world.

Police barred foreign journalists from entering the square and threatened them with violence, even barring them from covering the daily raising of the national flag.

Chinese and foreign tourists were allowed into Tiananmen as usual, although security officials appeared to outnumber visitors.

Dissidents and families of victims were confined to their homes or forced to leave Beijing as part of sweeping government efforts to prevent online debate or organized commemorations of the anniversary.

But in Hong Kong's Victoria Park, a crowd chanted slogans calling for Beijing to own up to the crackdown and release political dissidents. Organizers estimated its size at 150,000, while police put the number at 62,800.

"It is the dream of all Chinese people to have democracy!" the throng sang.

Hong Kong is one of the few places in China where the events of June 1989 are not off-limits, because the territory - returned by the British 12 years ago - operates under a separate political system that promises freedom of speech and other Western-style civil liberties.

"Hong Kong is China's conscience," Hong Kong pro-democracy lawmaker Cheung Man Kwong told the demonstration.

In the candlelight, speakers recalled the terrifying events in Tiananmen, where a military assault killed hundreds who had gathered for weeks in the square to demonstrate for freedom and even erect a makeshift statue of liberty.

Those killed were eulogized as heroes in the struggle for a democratic China, their names read aloud before the crowd observed a minute of silence.

"Hong Kong is the only place where we can commemorate, and we have to repeat this every year so our younger generations don't forget," said Annie Chu, 36, a Hong Kong tourism worker.

Earlier in the day, the central government ignored calls from U.S. Secretary of State Hillary Rodham Clinton and even Taiwan's China-friendly president for Beijing to face up to the 1989 violence.

The extraordinary security in Beijing came after government censors shut down social-networking and image-sharing Web sites such as Twitter and Flickr and blacked out CNN and other foreign news channels each time they showed stories about Tiananmen.