Visitors to the vast plaza in central Beijing were stopped at checkpoints and searched, and foreign television crews and photographers were firmly turned away. Uniformed and plainclothes officers seemingly outnumbered tourists.

A few pursued TV cameramen with opened umbrellas trying to block their shots — a comical dance that was broadcast on CNN and the BBC. There was no flicker of protest. Other than the intensive police presence and the Government’s blockage of some popular Internet services, the scorching hot day passed like any other in the capital.

In Hong Kong, throngs gathered at a park on Thursday evening for an enormous candlelight vigil on the 20th anniversary of the Tiananmen Square protests. Organisers said that 150,000 people joined the vigil, tying the record set by the first anniversary vigil in 1990 and dwarfing every vigil held since then. The police estimated the crowd at 62,800, their largest estimate for any vigil except in 1990, which they put at 80,000.

Hong Kong, returned by Britain to Chinese rule in 1997, is still semi-autonomous and is the only place in China where large public gatherings are allowed to mark the anniversaries of the 1989 protests and killings.

The peaceful assembly spilled out into nearby streets, shutting down traffic. Inside Victoria Park, thousands listened to songs and speakers who recounted the events on the night of the crackdown. Half-hour into the vigil, the lights in the park were extinguished and the attendees lighted a forest of white candles in inverted conical paper shields.

China’s Government has tried hard over the years to obliterate the memory of the huge student-led protests that shook the Communist Party and captivated the world for weeks.

An official reacted angrily on Thursday to a call by US Secretary of State Hillary Rodham Clinton for a full public accounting of the incident.

“The US action makes groundless accusations against the Chinese Government,” a Foreign Ministry spokesman, told reporters at a regular briefing. “We express strong dissatisfaction.”

President of Taiwan Ma Ying-jeou who has fostered closer ties with the mainland, also urged China to confront the episode. “This painful period of history must be faced with courage and cannot be intentionally ducked,” he said.

The remarks contrasted with the public silence throughout China. There was no mention of the day’s significance in Thursday’s Beijing newspapers. The state-run mass-circulation China Daily led with a story about job growth signaling China’s economic recovery.