The national flag in Tiananmen Square in central Beijing flew at half mast after a ceremony at dawn. The Olympic torch relay, currently on its domestic leg ahead of the Aug. 8 opening in Beijing, will likewise be suspended for three days.

"I have come today with a heavy heart," said Liu Xianzeng, watching the ceremony in Tiananmen Square. "I feel for the victims of the earthquake and soldiers who are helping there."

Around the country air raid sirens and car, train and ship horns will also sound to "wail in grief" at 2:28 pm (0628GMT), the time the quake hit a week ago, the official Xinhua news agency said.

On the eve of the official mourning period, a fresh tremor in south-western China killed three people, injured 1,000 and sent thousands fleeing their homes into the streets.

The tremor, one of the strongest aftershocks since the May 12 earthquake, hit Jiangyou city in Sichuan, Xinhua said.

It was 5.7 in magnitude and brought down a large number of houses, damaged 377 km (235 miles) of roads and six bridges, rescue authorities said late on Sunday.

The official death toll stands at nearly 32,500 from the original quake of 7.9 magnitude that rattled Sichuan province.

Some 220,000 people are reported injured and a further 9,500 are thought to be still buried under the rubble in Sichuan. Most are feared dead.

Officials have tried to keep people from the area because of aftershocks and a build-up of water in blocked rivers.

Xinhua said the most dangerous mass of water was only about 3 km upstream from Beichuan town where rescue workers saved a man on Sunday from under the remains of a hospital.

China says it expects the final death toll to exceed 50,000. About 4.8 million people have lost their homes.

SURVIVOR'S LEGS AMPUTATED

Late on Sunday, a woman was also pulled out of the rubble in Yingxiu after a 56-hour rescue operation during which her legs were amputated, Xinhua reported. A man was earlier found alive in a collapsed office building in Maoxian county, it said.

The military moved to quell concerns over the safety of its nuclear facilities, including the main nuclear weapons research laboratory, close to the affected zone.

Offers of help have flooded in and rescue teams with sniffer dogs and specialised equipment from Japan, Russia, Taiwan, South Korea, the United States and Singapore are assisting. Donations from home and abroad have topped 6 billion yuan ($858 million).

Statistics from past earthquakes show some victims have survived up to nearly a fortnight under rubble.

Yet Fujiya Koji, head of the Japanese rescue team in Sichuan, conceded: "Generally by this stage the likelihood of survival is low. They say they have been finding some in Beichuan and we'll certainly keep trying."