Rescuers searching for survivors from twin earthquakes that struck southwestern China battled blocked roads and downed communications Saturday as the death toll rose to 80.

Scores of people were leaving their homes in the mountainous border area of Yunnan and Guizhou provinces amid fears of further aftershocks as volunteers with supplies streamed in the opposite direction.

Some 820 people were injured and 201,000 displaced after two 5.6-magnitude quakes struck the resource rich but impoverished region on Friday, prompting the government to pledge 1.05 billion yuan ($170 million) for relief work.

Premier Wen Jiabao, who visited the worst-hit Yiliang county in Yunnan overnight, urged rescuers to redouble efforts in the crucial first 72 hours.

"Rescuing people is the top priority," he said in comments broadcast on CCTV news as he visited hospital patients and other survivors before flying back to Beijing.

Government aid would go toward providing for survivors' temporary shelter and medical care as well as rebuilding homes, roads and other infrastructure, the China News website quoted the finance ministry as saying.

Families staying in tents said they feared their homes were no longer safe.

"The house kept shaking and as I have four children, I couldn't stay there any longer," said a man surnamed Qing who described the earthquake as "terrifying".

Parents walked around carrying babies and bundles of possessions on their backs. Others took bowls of instant noodles from relief workers and queued to fill them with hot water.

Ambulances in Yiliang pressed through the crowds while rushing survivors to the hospital.

The death toll may yet rise as crippled infrastructure has made it difficult to collect information, a provincial official told state news agency Xinhua.

The Global Times newspaper said the earthquakes highlighted China's continued vulnerability to natural disasters, despite decades of rapidly improving wealth and living standards in much of the country.

"A quake as strong as Friday's... could have caused fewer or even no casualties in a more developed region," it said.

The hard-hit Maoping village surrounded by near-vertical cliffs had been evacuated as crumbling rock continued to fall. Giant boulders had crushed the road and vehicles.

On Zhaoyi Road, a mountain pass littered with rocks, heading toward Yiliang, families congregated outside their homes, looking reluctant to go inside.

While some left by foot with their meagre belongings, others boarded coaches, looking frail and tired. Volunteers, meanwhile, drove toward the disaster zone carrying food, water and other supplies.

One makeshift volunteer vehicle -- a hotel minibus from a nearby town -- was adorned with a red banner saying: "We will keep moving to provide help."

About 4,000 armed police and reserve forces have arrived to do rescue work, the Yiliang government said on its website, while another 600 workers have been sent by the State Administration of Work Safety, Xinhua said.

Authorities have sent 21,000 tents, 31,000 quilts and 26,000 coats to Yunnan while the Red Cross Society of China has also dispatched supplies.

Various institutions have donated as much as five million yuan ($800,000) to the relief efforts, the Yiliang government website said.

A hospital in Zhaotong city, which oversees Yiliang, got so busy that it set up 10 tents as makeshift wards. Photos posted on the Yiliang government website showed patients lying on cots while others waited on plastic stools outside.

Rain is expected in the next few days, which could further hamper rescue work by causing mudslides. Another concern is the possibility of disease after thousands of cattle were killed after sheds caved in.

The US Geological Survey said the first quake struck at 11.20 am (0320 GMT) at a depth of around 10 kilometres (six miles), with the second quake around an hour later.

Residents described how people ran outside buildings screaming as the two shallow quakes hit an hour apart around the middle of the day.

"I was walking on the street when I suddenly felt the ground shaking beneath me," posted one witness on Sina Weibo, a microblog similar to Twitter. "People started rushing outside screaming, it still scares me to think of it now."

The disaster is estimated to have damaged or destroyed 6,600 homes and cost 3.7 billion yuan ($580 million) in direct economic loss, the Yunnan civil affairs department told state media.

Southwest China is prone to earthquakes. In May 2008, an 8.0-magnitude tremor rocked Sichuan and parts of neighbouring Shaanxi and Gansu provinces, killing tens of thousands and flattening swathes of the province.

The Global Times said that after the latest quake, authorities should emphasise safety and sustainability in future developments.

Corner-cutting in construction projects leading to shoddy buildings, especially schools, was blamed for the death toll being as high as it was in the 2008 Sichuan quake.

"Many would prefer bigger, rather than safer but more expensive, houses or apartments," it said.

"To take the time and invest money in the prevention of natural disasters, which are unpredictable and are unlikely to occur, does not seem like a persuasive proposal to many in China."