Chinese security personnel are on heightened alert in Tiananmen Square on the 25th anniversary of the Beijing massacre, as memorials are held in Hong Kong. (Reuters)

Chinese security personnel are on heightened alert in Tiananmen Square on the 25th anniversary of the Beijing massacre, as memorials are held in Hong Kong. (Reuters)

— It was a quiet day in Tiananmen Square. Even as tens of thousands gathered in Hong Kong and global headlines marked the 25th anniversary of China’s brutal crackdown on student protesters, there was no trace of remembrance at the site where many of them were killed.

Tourists posed for pictures below the iconic portrait of Mao Zedong. Children ran laughing through the square.

The only sign of that day’s lingering effects: swarms of police officers patrolling the square and stationed every few hundred feet on the roads leading to it.

(Read: Here’s how Tiananmen lives on, 25 years after the bloody crackdown)

For weeks, as the anniversary approached, security in Beijing grew tighter. Foreign journalists were called in and warned. Officials mobilized tens of thousands of informants to look for suspicious activity, according to state media.

1 of 11 Full Screen Autoplay Close Skip Ad × Tiananmen Square Crackdown View Photos On June 4, 1989, hundreds — and perhaps thousands — of Chinese pro-democracy demonstrators were killed when tanks rolled into Tiananmen Square in Beijing to crush a student-led protest that had lasted six weeks. Caption 25 years ago, on June 4, 1989, hundreds of Chinese pro-democracy demonstrators were killed when tanks rolled into Tiananmen Square in central Beijing to squash a six-week long, student-led protest. June 3, 1989 A dissident student asks soldiers to go back home as crowds flood into central Beijing in this photo taken on June 3, 1989. After the violent suppression of the demonstrators, the government initiated a propaganda effort to quell popular discontent and remove evidence of the military attack and public resistance to it. Catherine Henriette/AFP/GETTY IMAGES Buy Photo Wait 1 second to continue.

Authorities jailed or forced out of the city dissidents most likely to criticize the government. By Wednesday, the heart of the capital was in lockdown.

This year, the repressive tactics ahead of the Tiananmen anniversary began earlier and were more extensive, a sign that the Communist Party views the historical event as an enduring threat.

The hushed interviews at the square Wednesday revealed just how effectively the party has quashed public memory of a crackdown that killed hundreds, if not thousands. Many claimed to have no remembrance of the massacre or appeared too afraid to respond.

“Today? What is special about today?” a 41-year-old tourist from Hunan province said in response to a query. When pressed whether he had not heard about an incident in 1989, he said nervously, “Oh, you mean the student protest back then? That was today? I had forgotten all about it.”

He then quickly walked away.

Three local college students — among the few who acknowledged the massacre and talked openly about it — said they had come to the square out of curiosity. Several police officers hovered nearby.

“Of course we know about June Fourth. It’s an open secret in China,” said one of the students, standing in the spot that 25 years earlier had been packed by a sea of protesters his age demanding political change.

But just because they knew about the massacre didn’t necessarily mean they agreed with the protesters.

“It was an irrational decision. Was it worth it to bleed and be killed for such a cause?” the student said.

Many former protesters , who witnessed those deaths, blame such reactions on the government’s propaganda, with classes and textbooks casting the 1989 protests as counterrevolutionary riots that threatened the country.

“This is why we, the survivors, must try our best to tell the next generation about our experience and help them achieve progress without sacrificing as much as we did,” said Xiang Xiaoji, 57, a former protester who now lives in New York.

In stark contrast to the silence in Beijing, tens of thousands in Hong Kong converged Wednesday night on Victoria Park for a candlelight vigil. Organizers said more than 180,000 people participated. The territory, a former British colony that returned to Chinese rule in 1997 but has a separate political system and greater liberties, has been a focal point of Tiananmen commemorations.

Under Hong Kong’s looming skyscrapers, rally organizers read out the names of those who died in the protests 25 years ago, including a 9-year-old girl. A wreath was laid beside replicas of the Monument to the People’s Heroes at Tiananmen Square and the Goddess of Democracy statue erected by protesters in 1989.

Speaking to the crowd, Teng Biao, a prominent human rights lawyer from the mainland, said that despite the many killed in Tiananmen, more have stood up for their rights in China. “You can’t kill us all,” he said.

Holding up candles, the crowd at one point repeated two chants: “Pass on this spirit from generation to generation” and “Fight to the end.”

One speaker, Lee Cheuk Yan, linked Tiananmen to Hong Kong’s struggles for democracy under Beijing rule. “The evil claw of Communist dictatorship is digging its way into our city, suppressing freedom, stepping up interference, manipulating the promised democratic elections,” he said.

In a statement, the White House said: “Twenty-five years later, the United States continues to honor the memories of those who gave their lives in and around Tiananmen Square . . . and we call on Chinese authorities to account for those killed, detained, or missing.”

Hong Lei, a Chinese Foreign Ministry spokesman, demanded that the United States “stop making irresponsible remarks related to issues of China’s internal affairs.” Hong said China had given its people great economic growth in the past 25 years.

Meanwhile, China’s repression of Tiananmen talk was also heavy online. Google’s search engine and applications were largely inaccessible this week, apparently the handiwork of authorities. The Chinese- and English-language Web sites of the Wall Street Journal also were blocked in recent days. Users of the professional networking site LinkedIn complained that it was censoring Tiananmen-related posts.

Human rights activist Hu Jia, 40, who participated in the 1989 protest, said by phone that he had been placed under arrest the past three months. “The dark side of society we are seeing today is the same that was shown 25 years ago,” he said. “The government believed they could monopolize power by taking all those lives before. Now, they control the power by arresting people, killing the freedom of dissidents. Nothing has changed.”

Among dozens of activists detained by authorities ahead of the anniversary was Yan Zhengxue, a painter featured in a Washington Post report Sunday about artists trying to keep alive the public memory of Tiananmen.

(Explore: What Tiananmen looked like then and now)

Before he was spirited away by authorities, he recounted being repeatedly forced by state security to leave Beijing on “vacations” ahead of sensitive dates such as Tiananmen anniversaries.

He described the awkward trips with his wife to rural areas accompanied by police, who he said were perpetually at the couple’s side to prevent them from talking to others or participating in events.

Reached by cellphone Wednesday, Yan confirmed in a brief conversation that authorities had again taken him out of Beijing.

“It’s not so convenient to talk now. There are people sitting with me,” he said.

Before hanging up, however, the 70-year-old quickly added, “They are so afraid at the moment. Even now, with someone like me, they remain afraid.”