Air raid sirens, and car, train and ship horns wailed and people stood for three minutes in silence on Monday to mourn the tens of thousands who died in last week's earthquake.

The moment of grief was observed across the vast country of 1.3 billion people at 2:28 pm, exactly a week after the devastating magnitude-8 quake struck Sichuan.

The death toll is estimated to be above 50,000.

The silent tribute was the first of its kind for citizens killed in a natural disaster.

President Hu Jintao and other members of the Standing Committee of the Political Bureau of the Communist Party of China Central Committee, as well as other officials pay a three-minute silent tribute to victims of the quake in the central government compound of Zhongnanhai in Beijing yesterday. The Chinese characters on the banner read: Deep mourning for Wenchuan quake victims. [Xinhua]

Flags were flying at half-mast across the country and all public entertainment has been suspended as the three-day mourning period started.

The Olympic torch relay is also suspended during the period.

From tent cities in Sichuan province to Beijing, cars, motorcycles and bicycles stopped on the road and sounded their horns. Pedestrians stood with their heads bowed.

In Tian'anmen Square the somber mood quickly turned into a vocal show of patriotism.

Thousands of flag-waving people chanted "Go China Go" and "Rebuild Sichuan", while singing the national anthem.

President Hu Jintao, who just returned from a three-day visit to the quake-hit areas, paid a three-minute silent tribute to victims of the quake in the central government compound of Zhongnanhai in Beijing.

At the ceremony that began at 2:28 pm, a sad and solemn Hu, in a dark suit with a white flower pinned to the chest, bowed under a national flag which was lowered to half-mast.

Hu was joined by colleagues in the country's top decision-making body, the Standing Committee of the Political Bureau of the Communist Party of China Central Committee, including top legislator Wu Bangguo and Premier Wen Jiabao.

Former president Jiang Zemin also stood in silence for the quake victims at a separate place in the city.

Vice-Premier Li Keqiang paid his tribute in Beichuan, Sichuan, one of the worst-hit regions. He was there overseeing rescue and relief work.

Across the country, people honored the quake dead in various ways: Some flew black kites, children stood with lit white candles, and villagers in the northwest burnt incense sticks and fake money in rituals to see off the dead.

Gong Zhen, a student who survived when the earthquake hit Beichuan county, cries as she attends a ceremony with around 500 students before resuming classes at a factory training centre in Mianyang, Sichuan province, May 19, 2008.  [Agencies]

In front of the Potala Palace in Lhasa, capital of Tibet, residents prostrated while saying prayers for the dead.

Rescuers, including those from Japan, Russia, the Republic of Korea and Singapore, took off their helmets and briefly halted their work in quake-hit areas.

The Shanghai and Shenzhen stock exchanges and the futures exchanges in Shanghai, Zhengzhou and Dalian suspended trading for three minutes from 2:28 pm.

Some of the stock traders said people volunteered to buy stocks of Sichuan-based companies to show their support, Xinhua reported.

China Central Television blacked out its screen for the three minutes.

Chinese diplomatic missions abroad also observed the mourning, some holding the silent tribute simultaneously despite the time difference.

Condolence books were opened in the Foreign Ministry and Chinese embassies and consulates around the world; and China's Permanent Mission to the United Nations held a solemn ceremony, which UN Secretary-General Ban Ki-moon attended.

In a demonstration of the international community's support, scores of foreign envoys and representatives of international organizations in Beijing visited the Foreign Ministry to convey messages of condolences.