EVEN THE MOST WARPED HORROR writers might not have thought up some of the scenarios facing the hundreds of thousands of residents and troops in China's Sichuan province this week.

Twisted roads and broken bridges, chemical spills, leaking dams, tourists stranded 2000ft up a cable-car line, and a fire burning for two days on a derailed freight train laden with petrol tankers were some of the first problems facing Chinese civilian and military rescue services after China's most devastating earthquake for 32 years.

In some towns, just a handful of structures were left standing more than a few feet above the ground. Many towns and villages were cut off for up to three days after the 7.9-magnitude earthquake knocked out all communications and transport links.

Eight passengers, including China Daily journalist Chen Jia, were trapped for four hours inside a crushed minibus that was perched over a steep drop into a river.

"I was jammed between the vehicle's back seat and my laptop, and couldn't move at all. My head was hanging down and became swollen," said Chen. "All of us were in shock but soon started to encourage one another."

Chen and the others were eventually pulled out by three local men who prised open part of the battered minibus. Thousands of others have far more gruelling tales of survival.

Some of the 140,000 troops leading relief efforts rescued more people from collapsed buildings on Saturday, including a German tourist and five South Korean students.

Peng Zhijun, a 46-year-old man who was rescued on Friday in Beichuan county, where about 80% of buildings collapsed, told state media he had kept himself alive by eating cigarettes and paper napkins, and using a shoe to collect and drink his own urine.

Peng fractured his left arm and was trapped beneath a fallen building. Speaking from hospital, he was quoted as saying that he strapped his broken arm to his head to relieve the pain.

"Then, I started thinking about how to eat and drink," Peng said. "I searched all over my pockets and only found half a pack of cigarettes and a few pieces of paper napkins. I broke the cigarettes into pieces and ate the powder. After the cigarettes were eaten up, I turned to the paper napkins."

Peng said he had hit a wall next to him many times to try to attract the attention of rescuers before he was finally found. Nine other people were buried with him on Monday, but six of them died over the next four days. Tens of thousands of people are believed to be still buried; most of them are likely to already be dead.

Troops in full battle dress wore surgical masks and carried long crowbars as they yesterday intensified their search of towns and villages in the mountains near Beichuan and Wenchuan counties, the epicentre of the earthquake.

A paramilitary officer who was one of the first outsiders to reach some of the worst-affected areas on Tuesday said that several towns in Wenchuan were almost razed to the ground.

Heavy rain had initially prevented helicopters from flying in emergency aid, while troops were still restoring badly damaged roads to the area.

The government currently estimates the likely death toll at 50,000. It raised the confirmed death toll to about 29,000 yesterday, and said that at least 10,000 people were still buried in a disaster zone that covers an estimated 40,000 square miles of mountains and valleys. Close to five million people are thought to have been made homeless by the quake.

Premier Wen Jiabao has been in Sichuan province since Monday to oversee relief work, flying by helicopter to some of the worst-hit areas.

President Hu Jintao joined him on Friday, as Wen said the government would do "whatever the country is capable of to combat the disaster".

"We won't give up even if there exists the slightest hope of finding more survivors," Wen said on state television.

Wen used a megaphone to address trapped residents of Juyuan town, where hundreds of children were buried at a middle school. "Please just hold on, people are going to get you out of here," he said. "If there's a glimmer of hope, we'll do all the best to save the people."

Hu Jintao toured the ruins of Pengzhou on Saturday, a city of 780,000 people where more than 100,000 homes collapsed. Several thousand people in outlying villages were still cut off after huge landslides.

The scale of the disaster prompted the government to allow foreign rescue services into China for the first time, with teams from Japan, Russia, South Korea, Taiwan and Singapore all working in Sichuan. The teams are equipped with sniffer dogs and fibre-optic cameras and heat sensors to detect people buried under the rubble.

The government has also allowed an unprecedented level of openness to foreign media, despite the People's Liberation Army controlling the earthquake zone.

But the first foreign rescue specialists only arrived from Japan on Thursday, and China declined offers of help from rescuers based in Britain and several other Western nations.

The Australian government offered a specialist urban search-and-rescue team, but China said that it was "unable to accept the offer as a result of logistical difficulties faced by the rescue operation".

The Red Cross says the final death toll could be as high as 100,000 and estimates about four million homes have been destroyed or damaged.

An International Red Cross relief co-ordinator, speaking from the town of Beichuan on Friday, said: "There are lots of dead bodies, with family members trying to identify loved ones.

"I can see at least 50 bodies covered by plastic sheets," he said, speaking from the Beichuan high school, where hundreds more students were still buried under rubble.

"There are people crying all around, still thinking there is a chance that their children are still alive.

"Rescue teams are still working on finding survivors but it is less likely that they will find any."

The mainly military rescue teams were "well organised" and working round the clock, while medical teams were "doing their best to provide care for the injured".

"There are doctors from all over China. I feel that we basically have the personnel and capacity, but need more resources and materials," he said.

The International Red Cross has appealed for $20 million to buy relief goods for 100,000 people in Sichuan.

Donations totalling $165m had poured in to the Chinese Red Cross by Friday, while the government allocated $500m for relief work and received another $454m from donors in China and foreign governments.

The earthquake was felt hundreds of miles away, with reports of shocks being felt in areas including Beijing, Shanghai, Hong Kong and Bangkok.

Most of the six million people of Chengdu, the Sichuan provincial capital, 60 miles from the epicentre of the earthquake, rushed outside as soon as they felt buildings shake.

"Everyone was sitting in the street," says Li Yang, a 49-year-old film director who was working in Chengdu on Monday. "I wanted to go the suburbs. I thought it would be safer because there are fewer high buildings, but I didn't know where to go.

"The local people I was with were worried as they had friends and relatives in the suburbs and couldn't get through by telephone."

Fearing aftershocks, most Chengdu residents slept on the streets on Monday night, many of them choosing the middle of main roads because they were the furthest places from tall buildings.

Hundreds of aftershocks have hit the province since last Monday's earthquake, the strongest one registering 6.1 on the Richter scale.

But a greater risk comes from hundreds of dams and rivers damaged by the earthquake. The environment ministry also ordered monitoring of radiation in case of leaks from several top-secret military nuclear facilities in the area, although international experts believe they are built to withstand powerful earthquakes.

Thousands of Beichuan residents fled to nearby hillsides yesterday after reports that a lake, formed when a landslide blocked a river above the town, was about to burst its banks. The government later said it planned to blast away part of the debris to allow water out of the lake and alleviate the risk of sudden major flooding.

At least 500 dams were damaged in Sichuan, including the large Zipingpu Dam on the Min river.

The US-based group International Rivers opposes China's "destructive dams and the development model they advance". It says Chinese seismologists warned in 2000 the Zipingpu hydro-power project should not be built because it was too close to the Longmen Mountains, a major tectonic fault line.

"Their warnings were ignored," International Rivers said on its website following the earthquake. "The Chinese government is building scores of large dams in the country's southwest, a risky proposition in an earthquake-prone area."

Rumours of polluted public water supplies have also caused panic in some areas. Police in Pixian county, Chengdu temporarily abandoned relief work to disperse a crowd of 10,000 people who surrounded government offices to demand information about reports of a leak at a nearby chemical plant.

At least 17 people have been arrested for allegedly spreading rumours about the earthquake, and the government has imposed temporary controls on food prices and transportation fares in Sichuan and three neighbouring regions to stop "hoarding and speculation".

Some media reports have claimed that the government had enough seismological data to issue a warning before the earthquake. They have focused on a 2002 report by Chen Xuezhong, a researcher with the China Earthquake Administration, who warned of the "virtual certainty" of an earthquake of at least 7.0 on the Richter scale in the area within the following few years.

A Chinese scientist also said in his online blog last week that semi-retired seismologist Geng Qingguo, known in China for accurately predicting the 1976 Tangshan earthquake, had also predicted the Sichuan earthquake.

Other reports claimed that cloud formations and an exodus of toads were clear precursors that government experts should have recognised.

But leading Australian seismologist Gary Gibson said he saw no significant precursory seismic activity.

"I had nothing unusual at all that you would regard as precursory," said Gibson, who works at the Seismological Research Centre in Melbourne.

"There were not even moderate events," he said of the period before Monday's earthquake, which international seismologists have upgraded to 7.9 on the Richter scale.

China's housing ministry on Friday ordered local authorities to investigate why 6898 school buildings collapsed in the earthquake.

More than 2000 children were buried under rubble at four Sichuan schools. Casualties at the collapsed schools were relatively high because the quake hit at 2.28pm on Monday when most students were in class, the ministry said.

Allegations of poor-quality construction and official corruption in the building of schools are widespread in many poorer inland areas such as Sichuan.

A UN expert said too many people were dying because of poor construction. "We know how to make buildings more resistant to earthquakes but this knowledge is still not yet well disseminated among decision-makers who enforce building codes for houses, schools and hospitals," Salvano Briceno, the director of the UN International Strategy for Disaster Reduction, said in a statement.

But the collapsed schools have produced many heroes in the fight to save lives, such as 21-year-old kindergarten teacher, Qu Wanrong.

Qu died while apparently saving a life by cradling one of the children under her body as she was trapped under a concrete slab in Sichuan's Zundao town, state media said.

At least 400 others died in Zundao, including more than 50 children and two more teachers from the kindergarten.

"Qu saved the child at the cost of her life," said Li Juan, the headteacher of the kindergarten.