Thousands of people are being evacuated from around a lake and a river at risk of bursting in southwest China's earthquake zone, disaster relief officials aid on Saturday.

The disaster relief headquarters in the Beichuan County told Xinhua that they received reports of water levels reaching danger point at the Laoyingyan section of the Qianjiang River on Saturday.

The river has been been blocked at several sections by landslides caused by Monday's earthquake.

"It hasn't burst yet, but we asked people to leave because we need to prepare for the worst," an official with the headquarters said.

He said experts were conducting aerial surveys of the river on Saturday and considering whether to blast the blockages to discharge the water.

Hundreds of rescuers and local residents were seen leaving Beichuan on Saturday. Injured people and old men were carried by the soldiers and fire-fighters on stretchers.

Xinhua reporter saw dozens of rescuers in Beichuan looking for survivors and disinfecting the area. The headquarters said 7,227 people died in Beichuan after the earthquake, about 5,894 people are missing, 4,459 are buried.