"As long as there is a glimmer of hope, spare no efforts in rescuing," the Party leadership ordered, according to Xinhua.
But the waves of rescuers appear to be hampered by lack of specialised equipment.
In the Sichuan town of Hanwang, huge cranes were working at some sites to clear demolished buildings, but at other sites residents picked through the rubble by hand.
Into the fourth day since the quake, hopes of pulling survivors from crushed homes, schools and factories dimmed.
In Dujiangyan, rescuers wrapped corpses dragged from the rubble in tarpaulins, and after allowing relatives to briefly mourn, sped them to morgues. They were so busy that a notice outside one collapsed school, where locals said 300 children died, asked parents to search for missing children in shifts.
"Because there is a heavy work load at the morgue we have arranged first for the parents of years 1, 2, 3 students to go and then organise for the parents of year 4, 5, 6 students," it said.
Offers of help were pouring in.
Blood banks in Beijing reached saturation point, with at least 3,300 people in the capital donated blood in a single day on Tuesday.
China also overlooked its hostility toward Taiwan, the self-governing island it sees as a breakaway province, to allow in chartered flights full of supplies. A Japanese relief team was also headed to Sichuan, China's Foreign Ministry said.
There were signs in some towns that more officials were arriving to organise the relief efforts, but many places were still a chaotic mess of makeshift tent cities.
DANGEROUS DAMAGE
The disaster area is home to China's chief nuclear weapons research lab in Mianyang, as well as several secretive atomic sites, but no nuclear power stations.
The China Nuclear Engineering and Construction Corp reported that several of its facilities in Sichuan were damaged by the quake, with six staff killed.
The report on its Web site (www.cnecc.com) did not describe the facilities or mention any radiation leaks. A Western expert with knowledge of the Mianyang lab said it was not likely the facilities were put at serious risk. He requested anonymity.
Landslides had blocked the flow of two rivers in northern Qingchuan county, forming a huge lake in the region.
"The rising water could cause the mountains to collapse. We desperately need geological experts to carry out tests and fix a rescue plan," Xinhua quoted Li Hao, the Communist Party chief of the county, as saying.
Premier Wen Jiabao, a geologist himself, has made emotional appeals from the disaster zone urging on workers and comforting orphaned children and was set to travel on Thursday to Qingchuan.
The quake was the worst to hit China since 1976 when up to 300,000 died.
