China rushed more troops and air-dropped relief supplies on Wednesday in areas cut off near the epicentre of the devastating earthquake in southwest Sichuan province as the toll mounted to nearly 20,000 with thousands of people still buried, trapped or missing.

As troops reached the quake-battered areas near the epicentre, the state media reported that the death toll in Mianyang city alone rose from 3,629 to 5,540 with 18,486 more buried and 1,396 missing.

In Yingxiu of Wenchuan county, only 2,300 people were believed to have survived out of 10,000 people living in the town near the epicentre, official Xinhua news agency said.  It had earlier reported a toll of over 12,000 in the quake.

Images: Of nature fury and shattered lives

The toll was expected to rise further once rescuers reach other towns in Wenchuan.

Some towns near the epicentre have been "razed to the ground" with no houses left standing, a police official was quoted by the state media as saying.

"The losses have been severe. Some towns basically have no houses left. They have all been razed to the ground," Wang Yi, head of an armed police unit sent into the disaster zone, was quoted as saying by Sichuan Online news site.

Around 20,000 soldiers had landed in the disaster-struck areas, another 30,000 en route by air, road and rail and on foot and the People's Liberation Army has ordered 30,000 more troops to reinforce the disaster relief, the agency said.

The first batch of elite soldiers from airborne special force were parachuted into Maoxian county. Inclement weather had initially hampered rescue operations.

Survivors desperately need medical help, food and water, officials were quoted as saying in Yingxiu, where people had to dig with their hands after cries for help were heard from under the debris of a school. Blocked roads prevented rescue teams and machinery from reaching the site. Rocks were still rolling down from the mountains. Military helicopters air-dropped food, drinking water and medicine in Yingxiu, Xinhua said. "Time is life", Premier Wen Jiabao told rescuers as he arrived at Beichuan county, one of the worst hit by Monday's deadliest earthquake in three decades, where the death toll is estimated between 3,000 and 5,000. Racing against time amidst flickering hopes, soldiers and civilians were still searching for survivors in Beichuan, a mountainous county, where the quake toppled 80 per cent of the buildings with 1,000 students buried under rubble of a six-storey school building.

"The ground was moving and I felt as light as a tree leaf. In a minute or two, I thought the ground cracked and the mountain slid and I lost consciousness. When I woke up again, rubbed my eyes and saw the whole county had disappeared in front of my eyes," the state media reported quoting a teacher who survived in Beichuan.

After reaching the quake-battered areas battling against inclement weather and damaged roads, rescuers were pulling out bodies from the heaps of rubble of schools, hospitals and houses, with hopes for survivors. Seven PLA helicopters had delivered 9.1 tonnes of disaster relief goods to Wenchuan and its neighbouring counties till noon. The supplies included satellite communication systems, medicines and quilts. The helicopters also carried 45 injured to hospital.

China's Air Force has also dispatched 10 transporters to send 50 medical teams from Beijing [Images], Shanghai and Xi'an for disaster relief. Several countries, including the US, Japan [Images], South Korea as well as the European Union and the United Nations have offered aid to China, which said it welcomes their help.

Chinese scientists are analysing images from a Japanese satellite of the areas jolted by the deadly quake, China National Space Administration said. They are the first large-scale images from space of the earthquake, Xinhua said.