Rescuers are continuing to comb through quake rubble in southwest China, after the expiry of the 72 hour "golden period" when finding survivors becomes much less likely.

Another 179 people were confirmed dead Wednesday, taking the death toll near to 600. Rescue is underway at a new site in Longtoushan, where dozens of residents and 20 vehicles were believed buried by landslide.

Most of the latest casualties were reported in Ludian and Qiaojia counties, where rescuers are concerned by the growing threat of barrier lakes, created when landslides block rivers.

QUAKE LAKE THREAT

Near the border of Ludian and Qiaojia, a barrier lake has led to the evacuation of 4,200 residents from the lower reaches of the Niulan River.

Sun Huaikun, who is in charge of the barrier lake response, said a reservoir on the upper reaches is intercepting river water to reduce pressure on the lake, while two hydropower stations on the lower reaches are speeding up the discharge of water.

The barrier lake is no small matter. It has has already flooded about 370 homes and residents have fled, leaving almost all of their belongings behind. Over 15 km long, it covers 49 sq km and the water level continues to rise, said Qiu Guangliang, head of the Huize County Water Authority. The army plans to use about 2 tonnes of dynamite to blow up blockage which formed the lake.

More houses will be submerged and more people will need to be rehoused as the water level rises, said Liang Zhiqiang, head of the Huize county government.

"Our village has been inundated," said Zhang Guoqiang, 36, from Xintian village. "We only took a few small things and moved to higher ground."

"The water level rose quickly. We had no time to take cash, quilts and grain from our house. Nothing is left. The house, crops and fruit trees were all submerged," said villager Liu Zongxiu.

Xiao Shuzhi, 72, from Laofangzi village, had never seen such a flood on the Niulan river. In the past few days, she and her family have kept watch on the rising water level to be ready to run to higher mountain areas at any moment.

ONGOING RESCUE

Rescuers and search dogs are now working in remote, sparsely populated areas and officials attribute Wednesday's sharp rise in reported casualties to the inaccessibility and remoteness of villages.

Downpours and traffic disruptions have put acute time pressure on rescuers and the likelihood of finding survivors declines every minute. On a ruined street of Longtoushan, an orange-clad soldier and her dog continue their search for survivors as helicopters hover overhead.

"The 'golden 72 hours' are up, but we'll keep with our mission and not give up hope," said Dai Yajuan, 23, of Chengdu Military Area Command.

On Monday, Dai and her colleagues recovered the bodies of three women from their collapsed home. Seventy rescuers from Dai's engineering corps have retrieved a dozen bodies.

On a heap of rubble, Wang Ping, 39, silently watches a group of police attempting to reach her husband and son buried in their home. On Tuesday morning, Wang saw the legs of her husband and a detector has located her son. Both were in the second floor when the building collapsed. A whole day has gone by and rescuers are still digging.

Nine people in Qiaojia are missing, 2,400 are injured and another 230,000 have been relocated but are still suffering water and food shortages.

Over 280 km of water pipes and facilities at 37 water sources have been damaged or destroyed, cutting off supply to over 300,000 people. Local bottled water plants are providing 50,000 liters of drinking water every day, a woefully inadequate volume for the number of people in need. In relocation centers in worst hit areas such as Longtoushan, residents can drink bottled water and have hot meals.

Zhou Minghui, head of Ludian's water bureau, said an emergency water distribution network should have been ready by Wednesday.

POVERTY, FRAGILITY

Survivors are risking life and limb to retrieve their belongings.

Chang Cheng, 28, found two books of his family tree in the debris. "My father died in the disaster. I know these things meant a lot to him. I don't care about all the other things left in our home," he said.

Wang Facai managed to recover 16,000 yuan (about 2,600 U.S. dollars), along with quilts and clothes from the ruins of his home and immediately put the cash in a nearby bank.

"Many survivors have begged us to help search for their property. Sometimes we had to say yes, even though it slows down our efforts to save people," Dai said.

The earthquake has revealed the acute poverty and fragility in the region, which appears pretty much unchanged, despite having been previously exposed by disasters of this kind.

In Ludian, nearly 60 percent of farmers live on less than 1 dollar per day and houses built with mud clay are the best they can afford.

A national plan to improve earthquake defense promised to make buildings in most urban areas resistant to 6.0 magnitude earthquakes, but in Yunnan, especially in remote areas, most infrastructure and houses are not resistant to earthquakes, said Zhang Junwei, a director of Yunnan earthquake administration, If villagers had money to rebuild and maintain their homes, less damage and fewer casualties would have resulted.

HOPING FOR MIRACLES

As the search goes on, "miracles" inspire optimism among rescuers. Two senior residents of Babao Village, aged 88 and 76, were pulled from the debris about 50 hours after the disaster. Both are in a stable condition.

Figures from the National Health and Family Planning Commission showed that 2,833 people had been treated for their injuries as of 4 p.m. Tuesday, with 1,295 of them hospitalized. Among those hospitalized, 122 are seriously injured and another 40 critically.

Yunnan is prone to earthquakes. A quake in Tonghai County killed 15,621 people in 1970 and another in Daguan and Yongshan counties in 1974 left 1,423 dead.