Rescue workers search for survivors in the rubble of collapsed buildings in Dujiangyan, in southwest China's Sichuan province, on Thursday. (Li Gang/Xinhua/Associated Press)

Chinese President Hu Jintao arrived in the devastated central province of Sichuan on Friday, state news agency Xinhua reported, as rescuers continued to dig for survivors and bodies near the epicentre of a massive earthquake that struck the country four days ago.

China's state cabinet said the death toll from Monday's 7.9-magnitude quake will likely hit 50,000, as tens of thousands of people are still believed to be trapped under the rubble in Sichuan.

Xinhua quoted Hu as saying the relief effort has entered into "the most crucial phase."

" We must make every effort, race against time and overcome all difficulties to achieve the final victory of the relief efforts," he said.

According to Xinhua, Hu will also meet with some of the thousands of troops and medical workers who have been trying to locate victims in a massive around-the-clock rescue effort.

More than 19,500 people have been found dead so far, an official death toll that jumped from 15,000 on Wednesday.

A survivor is helped out of the rubble in Mianyang city in Beichuan county on Thursday. (Takanori Sekine/Kyodo News/Associated Press)

The Chinese government has issued a plea for heavy machinery on its website, asking for donations of cranes, hammers, shovels and demolition tools.

Roads in the epicentre area, in Wenchuan in northwest Sichuan, are being cleared of debris, allowing rescue teams made up of about 130,000 police, soldiers and volunteers to bring in heavy machinery. Up until Thursday, most rescuers had been digging for survivors by hand.

"This is only a beginning of this battle, and a long way lies ahead of us," Gao Qiang, the vice health minister, told reporters in Beijing Thursday.

After more than 72 hours, rescuers fear the possibility of finding people alive in the rubble is getting slimmer, as trapped survivors run out of water and food.

Still, there have been miracles. A rescuer told the CBC's Anthony Germain that he could hear a girl murmuring "save me, save me" from under a heap of concrete slabs at a collapsed school in the city of Dujiangyan.

About 800 children died when the school collapsed, and the rescue worker said if he hadn't pulled the girl out from the rubble alive, her voice would have haunted him forever.

"The devastation almost defies description," Germain said from Dujiangyan. "Everything here is in splinters."

He said the earthquake levelled a large number of schools in Sichuan province, killing thousands of students.

Quake affected 10 million people, destroyed 4 million homes

The Chinese government estimates that 10 million people have been directly impacted by the quake, with four million homes shattered, many in the Sichuan county of Beichuan.

"This whole county has been destroyed; basically there is no Beichuan county anymore," said Gu Qinghui of the International Federation of Red Cross.

Survivors who are free are scrambling to find food and shelter. In Dujiangyan, they are sleeping under plastic tarps outside their damaged homes, afraid to return inside. Those who own cars and motorcycles can't drive away because gas stations have run dry and are closed, Germain said.

In the town of Luoshui, mechanical shovels are being used to dig pits deep enough to bury all the dead.

The official Xinhua news agency said three mountainous towns north of the Sichuan provincial capital of Chengdu were still cut off.

It said 20,000 residents were trapped in the towns of Qingping, Jinhua and Tianchi and the number of people killed or injured was not known.

Two Médecins Sans Frontières teams have been assessing the immediate health needs of quake survivors in several affected areas of Sichuan.

They say there is an urgent need for shelters, drinking water, sanitation equipment and medical supplies. Most pharmacies in the area were destroyed by the quake, and people are facing a dire shortage of medicines.

Another MSF team visited the area of Pengzhou, located about 40 kilometres north of Chengdu. There were reportedly hundreds of injured people in two towns in the neighbouring Longmen mountains.

Across the earthquake zone, many hospitals were obliterated or rendered unsafe. Numerous makeshift care centres have sprung up on the front lines of badly damaged towns. But they are overwhelmed with the number of injured still pouring in from the hardest-hit areas.

'What do we need? We just need some rest.'— Wu Tianfu, doctor

"What do we need? We just need some rest," said Wu Tianfu, a doctor at a tent set up by the Red Cross Society of China in the town of Hanwang, where hundreds of schoolchildren died.

"Then we need gloves, masks, iodine, sutures, cold medicine," said Wu. "It's a long list."

There are additional sources of fear — like the 391 dams that were structurally damaged in the quake and are at risk of breaking down, and the two chemical plants that collapsed in the town of Yinghua, releasing 80 tonnes of ammonia into the ground, forcing 6,000 people to leave.

More than 100 helicopters have been deployed to the quake area, and the military plans on airdropping 50,000 packets of food and 5,000 blankets into badly hit areas.

"The survivors are literally streaming out of the mountains and they tell tales of destruction and death that are just horrendous — thousands of people dead in the rubble and others running for their lives," said the CBC's Michel Cormier, also reporting from the area.

China has accepted an offer from Japan to send in a rescue team, according to a statement by foreign ministry spokesman Qin Gang. China's long-time rival, Taiwan, is sending a cargo plane filled with tents and medical supplies to the Sichuan capital of Chengdu.

The Red Cross has issued an appeal for medical supplies, food, water and tents.

So far, $125 million US in donated cash and goods have come into China from around the world.

With files from the Associated Press