A 6.1-magnitude earthquake has shaken Sichuan province in China five days after a massive tremor killed tens of thousands of people.

The US Geological Survey reported the latest earthquake, which follows scores of slightly less strong aftershocks during the week.

It was nearly 50 miles deep and hit 49 miles west of Guangyuan.

The quake hit as thousands of Chinese fled their homes amid fears a lake could burst its banks, hampering rescue efforts after Monday's 7.9 earthquake killed about 29,000 people.

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

President Hu Jintao urged rescue workers to continue their efforts, saying: "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".

Survivors were still being found including a German tourist who was pulled from rubble in Wenchuan after being buried for 114 hours.

Thousands fled a Chinese county near the epicentre of the earthquake amid fears a lake had burst its banks.

Confusion caused panic after reports suggested water levels were rising rapidly, prompting thousands to flee to the hills to escape possible flooding. The reports were later found to be untrue. Some 1.2 million people were being evacuated in Qingchuan, about 90 km (55 miles) northeast of Beichuan.

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.

China has sent 130,000 troops to the disaster area, but roads buckled by the quake and blocked by landslides have made it hard for supplies and rescuers to reach the worst-hit areas.