Yet some slivers of hope remained, among them the dramatic rescue of a woman who was pulled out alive from the debris 67 hours after the quake.
Rescue efforts in the southwestern province of Yunnan, where the 6.1-magnitude quake struck Sunday, were heavily hampered by traffic delays and landslides blocking roads.
At least 589 people had been confirmed killed as of Wednesday morning, China's ministry of civil affairs said on its website, marking a sharp increase in the death toll.
The ministry added that 2,401 people were injured and 230,000 had been evacuated, while more than 80,000 homes had fully or partially collapsed.
In one tale of good news from the disaster zone, rescuers freed a 50-year-old female survivor from underneath a pile of rubble on Wednesday afternoon, where she had been trapped for almost three days.
Liao Tengcui was conscious at the time of her rescue, although she had suffered from "serious injuries" and was unable to move her left leg, the official Xinhua news agency reported.
Two others -- a 76-year-old man and an 88-year-old woman -- were also pulled out alive Tuesday night.
No explanation was given for the sudden increase from a toll of 410 given on Tuesday, though rescuers have steadily been pulling corpses from the wreckage.
"This has been terrible, I have lost colleagues, friends and witnessed so much tragedy," doctor Shang Gangzheng tearfully told AFP in Longtoushan, at the epicentre of the quake.
Around 150 blue tents have been set up in the township to provide shelter for survivors, with litter strewn across the site and a strong smell of urine emanating from a tiny creek at the back.
Distraught mothers sought to comfort each other over the deaths of their children.
"I lost my seven-year-old daughter and 10-year-old son in the earthquake," said Yan Anqiao, 30, staring at the floor.
"I am not sure if I can ever have a real home again without my children."
The girl and boy were "the world, everything" to her, said the now childless mother.
Sheng Taimei had gone out while her 11-year-old daughter, who had stayed at home to do housework, was killed.
"She was so helpful to me. She was very warm, full of emotion," she said. "I am lost without her."
Search efforts in Longtoushan were being concentrated in a 600-metre (0.4-mile) swathe of hillside in the township's central urban area.
Residents in the area told AFP that school dormitories had collapsed in the quake, echoing a 2008 disaster in Sichuan which killed more than 80,000 people, thousands of them children who died as their cheaply built schools crumbled.
'Unfit for use'
China called for civilian volunteers to stay away from the disaster zone as traffic blocked supply routes and "substandard" relief goods flooded into the area.
More than 18,000 professional rescuers have headed to the disaster zone, state media said, most of them military and police.
But huge tailbacks have developed around the worst-hit areas, mainly consisting of cars driven by members of the public bringing in supplies or offering help.
Workers have also been halting traffic to set off explosions on the mountainsides to dislodge huge boulders perched precariously over roads.
Pang Chenmin, head of the ministry's disaster relief bureau, urged the public to avoid the disaster zone as the 72-hour "golden period" for rescue drew to a close.
"In order to ensure the best chances of rescuing survivors, we advise non-professional groups and volunteers against entering the quake zone by themselves so as not to cause traffic and communication difficulties," he said, according to Xinhua.
Many volunteers who walked or hitchhiked to Longtoushan have slept out in the open, or entered tents used by survivors.
Some brought their own vehicles into the worst-hit areas, carrying in goods such as fizzy drinks.
"Some relief materials are unfit for use in disaster areas, some are substandard products, some are overly abundant and take up precious space and traffic resources," added Pang.
Some civilian volunteers, who had arrived with little or no equipment, were already leaving the zone.
The 2008 Sichuan disaster -- China's worst quake since 1976 -- sparked a wave of public sympathy and a huge volunteer rescue effort.
Subsequent earthquakes have seen problems with volunteers, who have sometimes been labelled "disaster gawkers" by Chinese media.
Unofficial vehicles have been banned around Longtoushan to relieve the traffic, but that did not stop volunteers entering the town on foot.
Jiang Xingxing, 18, said she walked for three hours with 21 other members of her organisation Safety for the Public Good.
"I don't really have any capabilities in first aid or rescue, but I just wanted to come to help people," she said, as her colleagues took photographs of reporters.