Thousands of Chinese fled their homes yesterday amid fears a lake could burst its banks, hampering rescue efforts after the deadliest earthquake in more than three decades killed about 29,000 people.

Rescue workers returned to Beichuan county, near the epicentre of the quake, in Sichuan province, but many residents were too frightened to return, nervous about a lake formed after aftershocks triggered landslides blocking the flow of a river.

"After briefly evacuating, rescue work returned to normal at Beichuan," an official website (www.china.com.cn) said, blaming the evacuation on a false alarm.

A paramilitary officer had told Reuters earlier that the likelihood of the lake bursting its banks was "extremely big".

The situation was "very dangerous because there are still tremors causing landslides that could damage the dam", said Luo Gang, a building worker who left the southeastern port city of Xiamen and rushed home to look for his missing fiancée.

Rescue work had been complicated by bad weather, treacherous terrain and hundreds of aftershocks.

As the weather becomes warmer, survivors were worried about hygiene and asked questions about their longer-term future.

There has been growing concern about the safety of dams and reservoirs which have been weakened in the mountainous province of Sichuan, an area about the size of Spain. In Sichuan and neighbouring Chongqing, 17 reservoirs were damaged, with some dams cracked or leaking water. Several are on the Min river, which tumbles through the worst-hit areas between the Tibetan plateau and the Sichuan plain.

The Lianhehua dam, built in the late 1950s northwest of Dujiangyan, showed cracks big enough to put a fist in.

China has said it expects the final death toll from Monday's 7.9 magnitude earthquake to exceed 50,000. About 4.8 million people have lost their homes and the days are numbered in which survivors can be found.

Cabinet spokesman Guo Weimin, taking a long pause to compose himself as he read from an updated casualty report at a news conference, put the death toll so far at 28,881.

A billboard on the road into Beichuan shows a picturesque hill town with a river snaking past. What remains after Monday's earthquake is a horror scene.

Navy medic Han Zhihai, walking into the near-deserted town from a camp nearby after taking a lunch break, points to a huge boulder, one of many by the dirt-covered road that careened down the adjacent mountain during the giant tremor.

"Legs," he says.

Jutting from under the rock are two legs, feet pointing down, one still wearing a purple high heeled shoe.

Further into town, some 90 km northeast of the epicentre of the quake, streets are buckled and cracked and every building is ruined in one way or another.

Some crumbled into unrecognisable piles of wood, concrete and bricks. Others came clapping down, the floors finally resting stacked like pancakes with no space in between. Many more buildings dropped largely intact from the second floor up, crushing the ground floor and everything in it.

"That used to be a school," one of Han's teammates said, pointing towards a giant pile of boulders and dirt that slid down a mountain. The only thing left standing was a flagpole with the national flag still flying.

"At some of these places it will be impossible to extract bodies."

Five days after the 7.9 magnitude earthquake struck, Han, his team of six, and hundreds of other soldiers and rescue teams from around the country are fighting fatigue but still carefully searching for survivors in one of the hardest hit areas.

Beichuan is eerie and deserted except for the rescue crews and a handful of residents calling out for loved ones or digging for them.

"We've been working about 20 hours a day. I haven't washed my face, I haven't washed my feet, I haven't brushed my teeth in three days," Han said on Friday.

"This is really difficult," said Zhang Mingye, a member of the team from the main navy hospital in Beijing. "But we have to do it. We have orders to follow. It's starting to get hard to find live ones now."

Time was running out, but there are still some survivors. Sichuan vice governor Li Chengyun said there were more than 14,000 people buried in rubble in the whole province. Earlier on Friday, Han's team tended to two children pulled from the wreckage of a school. By late afternoon, Xinhua news agency said 17 people had been rescued from the ruins of Beichuan.

Rescue squads in orange jumpsuits still picked through the remains of several buildings where calls for help have been heard. Sniffer dogs and electronic devices help locate the living among the rubble.

Han's team stopped before a broken building where a crew of rescuers from the eastern province of Jiangsu were working.

One shouts: "Do you have anyone living in there?"

"Yes. Two," replied a rescuer.

"How long before you'll have them out?"

"I don't know," was the reply.

Han's team decides to move on in search of others.

"Look around," said Zhang as he walked down an uneven concrete road with contorted buildings on each side, some leaning in, some leaning out, others half pulverised.

"You can imagine that this was a fairly well-off place before the earthquake. Now, I doubt one per cent of its people have survived."