* China begins three days of mourning

* More than 34,000 dead

* China estimates losses in Sichuan at $9.6 billion (Adds details)

By Lucy Hornby

PINGTONG, China, May 19 (Reuters) - From tent cities in Sichuan province to Beijing's Tiananmen Square, sirens wailed and millions of Chinese stood for three minutes 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 p.m., exactly a week after the 7.9 magnitude quake that ravaged the southwestern province of Sichuan.

"I think the three minutes was important because it means that everyone, from the central government down to every individual, is thinking of us. Because this is worse than a war," said He Ling, a policeman in Pingtong town, which was almost totally wrecked by the earthquake.

Even as the rescuers stopped work, another aftershock rattled the area and set off a small landslide from a nearby cliff.

The army and the medics lined up with bowed heads and a huge Chinese flag was waved from a large pile of rubble.

The death toll from the quake was raised to more than 34,000 on Monday, but the figure could jump dramatically as the Communist Party chief in Sichuan said nearly 30,000 were missing. A further 5,000 are believed still buried under the rubble.

The government put direct economic losses in Sichuan alone at about 67 billion yuan ($9.6 billion).

Air raid sirens, as well as car, train and ship horns wailed around the country to mark the one-week anniversary. Flags flew at half mast and cinemas were ordered to stop showing films for the mourning period.

In Beichuan, another town devastated by the quake, several hundred rescuers bowed their heads and laid wreaths made from twigs and scrap paper pulled from the debris.

"We're all feeling very heavy hearted. So many people weren't saved," a soldier said, by the remains of a wrecked school.

In Beijing, the country's top leaders, led by President Hu Jintao, wore white flowers on their chests and bowed in silence.

Nearby, in Tiananmen Square -- where student-led pro-democracy protests were crushed by the army in 1989 -- the sombre mood quickly turned into a vocal show of patriotism. About 1,000 flag-waving people marched in the vast square, chanting "Go China Go" and "Rebuild Sichuan", and singing the national anthem.

SEARCH FOR SURVIVORS

A senior government official said rescuers had reached the remotest areas of the province by Monday, but roads to some 50 quake-hit towns and villages were still blocked by rocks and mudslides.

Hundreds of aftershocks and bad weather have hampered the rescue operations, and officials have warned of rockslides from unstable mountain slopes, and blocked rivers threatening to burst their banks.

More than 200 relief workers in five vehicles were buried by mudflows over the weekend, while trying to leave quake-affected areas, Xinhua said, citing the transport ministry. The death toll had not been confirmed.

There was a burst of elation in ruined Beichuan, when one woman was found alive.

Wang Hongguo, head of the rescue team, said she had found her under a mass of concrete. "We had to pull her out very gradually. She looked quite sturdy, so she might pull through," Wang said.

But rescuers mostly had the gruesome job of recovering decomposing bodies. Dozens of bodies were pulled from the rubble in Beichuan on Monday, and rescuers scattered lime and splashed disinfectant to prevent disease.

Farmer Wang Hongchen and his wife Chen Guangfen scrambled over hundreds of metres of rubble to look for their son, who worked as a mobile phone repair man in the town.

"I think there's still hope. He worked on the first floor, so if he was lucky there would have been space for him to survive," Wang said, in between shouting out his son's name over the ruins.

Some 245,000 people were injured in the disaster, the worst to hit China since 1976, and Premier Wen Jiabao on Monday ordered stepped-up epidemic prevention work, Xinhua reported.

Authorities set up an initial batch of 300 "tent classrooms" offering psyschological counselling to schoolchildren in the quake-affected areas of Mianyang and Deyang, Xinhua said, citing the Education Ministry.

On Monday, the Foreign Ministry appealed to the international community to provide more tents for about 4.8 million people who lost their homes in the quake.

So far, 10.8 billion yuan ($1.55 billion) has been received from donors at home and abroad, China said. Chinese customs had cleared 81 shipments of relief materials from 17 countries by Monday, including satellite telephones, medical equipment and spare parts for helicopters.

Rescue teams from Russia, Japan, Taiwan, South Korea, the United States and Singapore are also searching for survivors.

($1=6.990 Yuan)

(Additional reporting by Chris Buckley in Beichuan and by Ben Blanchard, Benjamin Kang Lim in Beijing; Writing by Jeremy Laurence and Ian Ransom)

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