Beichun, May 17: A Chinese county near the epicentre of a 7.9 magnitude earthquake was ordered to evacuate on Saturday amid fears a lake had burst its banks, prompting thousands to flee to the hills to escape possible flooding.

Forty-six seriously injured people were in "dire need of help" in Beichuan, where the official Xinhua news agency said earlier the water level was rising rapidly and "may burst its bank at any time".

It did not give details but Hong Kong cable television said some 1.2 million people were being evacuated in Qingchuan, about 90 km northeast of Beichuan, as rising waters threatened to burst a lake's banks there.

A witness said by telephone the military was evacuating everyone in Beichuan, even rescue workers.

This journalist fled a place near the Beichuan Middle School, which President Hu Jintao visited on Friday. Soldiers were talking on the radio saying 'all retreat' and there was a lot of dust in the air. The soldiers were leaving fast.

There has been growing concern about the safety of dams and reservoirs which have been weakened in the mountainous province of Sichuan, an area about the size of Spain.

Wenchuan after being buried for 114 hours, Xinhua said.

China has put the known death toll at over 22,000 but has said it expects it to exceed 50,000. About 4.8 million people have lost their homes and the days are numbered in which survivors can be found.

"Although the time for the best chance of rescue, the first 72 hours after an earthquake, has passed, saving lives remains the top priority of our work," Hu told distraught survivors just over a week after a jubilant China celebrated the Olympic torch reaching the summit of Mount Everest.

In earthquakes elsewhere in the world, survivors have been found a week or more after the disaster. In Baguio in the Philippines in 1990, a cook was found alive in the rubble of a shattered hotel after two weeks.

He had drunk his own urine and drops of rainwater to stay alive. A man and a woman trapped for 11 days in an elevator shaft in the hotel were also rescued.

Among other survivors on Saturday, Xinhua said 33 people were dug out of the rubble in Beichuan, one of the worst hit areas. One young man was rescued after being buried for 104 hours and troops evacuated 18 scientists trapped in a forest in Mianzhu.

Premier Wen Jiabao said the 7.9 magnitude quake was "the biggest and most destructive" since before the Communist revolution of 1949 and the quick response had helped reduce casualties.

That compares even with the 1976 tremor in the northeastern city of Tangshan which killed up to 300,000 people.