Almost five million people have been left homeless by Monday's devastating earthquake in China's south-western Sichuan Province, officials say.

They said the extent of the problem only became clear when communications were restored.

So far, 22,069 deaths have been confirmed and thousands remain missing. It is feared up to 50,000 may be dead.

Chinese President Hu Jintao, visiting the province, said rescue work was at its most crucial phase.

Premier Wen Jiabao said the quake was the most destructive and widespread since the People's Republic was founded in 1949.

Its scale was greater than that of the Tangshan earthquake in 1976 which left 240,000 dead, he said.

China has announced an investigation into why so many schools have collapsed.

Further aftershocks - one measuring 5.9 - continued to strike the area, causing landslides that buried vehicles and knocked out communications only just restored.

'Top priority'

Sichuan Vice-Governor Li Chengyun said 4.8 million people were now in "temporary shelter" following the earthquake.

Local officials said the extent of homelessness in the region only became clear on Friday.

"Before today, communications and roads to some cities and counties in the province were cut off because of the quake," the official told AFP news agency.

"That's why the number has increased so fast now that links have been restored with the cities and counties."

As the search for survivors continued intensively on Friday, four people were reportedly pulled out alive.

Four days after the quake, Chinese CCTV showed pictures of a five-year-old boy, looking weak and bruised, being taken from the rubble, bandaged and strapped to a stretcher.

Meanwhile, a 23-year-old nurse was rescued from the ruins of a hospital, and two survivors were found buried together beneath a collapsed office building in the shattered district of Beichuan, state news agency Xinhua reported.

Mr Wen, who has been in the area since the earthquake struck, said the focus of the effort was still reaching survivors.

"Saving lives is still our top priority, as long as hope of survival still exists," he said.

Foreign rescuers

The Chinese president's presence in the region appears to reflect the level of government concern over the scale of the disaster.

"The challenge is still severe, the task is still arduous and the time is pressing," said Mr Hu.

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

BBC news