With factory hooters and car horns blaring, China began three days of national mourning for the 50,000 dead of the Sichuan earthquake.

Rescue work stopped on hundreds of collapsed buildings in devastated towns and villages at 2.28pm, a week to the minute after the ground began to shake across the province.

In streets and squares, people stood with heads bowed, led by state leaders lined up outside the central government offices.

Afterwards, in Tiananmen Square in Beijing and in the main square in Chengdu, Sichuan's provincial capital, thousands staged patriotic demonstrations.

They punched the air and shouted "Zhongguo Jia You" – "Go! Go! China" – in apparently spontaneous attempts to boost national morale.

In the towns that have taken in hundreds of thousands of refugees from the earthquake zone, the atmosphere was more subdued.

Among the most poignant scenes was the main hall of a television factory in Mianyang, a city of 800,000 people which is also now home to the remaining population of Beichuan county.

Beichuan is one of the worst hit places, with several schools completely demolished in the town and residents of remote villages still clambering over broken roads to find aid.

The factory has been turned into a camp for middle school students who have lost their families, in the hope that it can be a focal point for parents looking for their children.

Each of the 860 students has been given a sleeping bag, a red hold-all for whatever remains of their possessions, and a small towel. As a siren sounded, hundreds of teenagers stood to attention in rows in front of beds made of cardboard strips.

A television set showed a ceremony live from Tiananmen Square, with the national anthem followed by the raising of the Chinese flag in front of the portrait of Chairman Mao that hangs over the entrance to the Forbidden City.

During the silence, it switched to pictures of rescue workers also standing to attention, ending with the site at Beichuan middle school, where 1,000 children are feared to have lost their lives.

Some of those in the Changhong factory were survivors from the school. Jiang Huaiqin, 17, said 39 of her classmates were killed.

"We were in a politics class when the building started swaying," she said. "The teacher started shouting. Three of us at the back ran for the stairs.

"We were on the fifth floor but we just managed to get out as the building collapsed."

Survivors continued to be pulled out of the rubble during the day, three in total. One was a 61-year-old woman, Li Lingcui, who was found in the wrecked market place at Beichuan, while another was an 80-year-old man.

State media gave a confusing account of another disaster, saying that 200 rescue workers had been buried in mudslides in the past three days. But it did not say how many had died, or where the incidents occurred.

The government said the total number of confirmed dead had risen to 34,073, while the provincial government said 9,509 people remained buried and 29,418 others were missing.

The authorities also issued a warning of an imminent magnitude 6-7 aftershock, causing brief panic on the streets of Chengdu, where people took to their cars in an attempt to escape the city.

As the chance of finding many more still alive in the rubble begins to fade, relatives of the missing keep alive what hope they have by hunting through refugee camps and hospitals.

Outside the camps lists are posted of those registered there and in nearby hospitals.

At one of the two main sports stadiums in Mianyang, both of which are full of survivors, a steady stream of people stood running their fingers down the names.

Next to the lists are pictures of missing children – and in some cases of children who are missing their parents.

"Teacher Liu" has posted photographs of five of his children from Liuhan Hope Primary School, aged from six to 12, for whom he is now caring.