Some 160,000 people have been evacuated out of the valley near Beichuan in the Sichuan province, from more than 30 townships.
Dozens of lakes were created by the magnitude 7.9 earthquake that hit central China and rains that followed. Officials fear these natural dams could crumble easily since pressure is building up behind them as water continues to pour in from streams and rivers.
In southern China, flash floods killed at least 20 people and left 16 missing, the official Xinhua news agency reported on Tuesday, according to Reuters. Torrential downpours have triggered flooding and landslides there.
Officials are concerned that summer rains will exacerbate the destruction caused by the quake, and could further pressure the weakened dams.
Authorities are frantically trying to drain hundreds of reservoirs and dozens of lakes that are in danger of bursting, the largest of which is the swiftly rising lake that triggered the evacuations, which is being called the Tangjiashan lake.
About 1,8000 soldiers have climbed through mountain passes to reach the lake and have been preparing to destroy parts of the barriers with explosives in an effort to control the flow of water.
State television also showed construction equipment being used to carve out a channel to drain the water, reported the Associated Press.
"We are prepared to get rid of the trees by chopping and explosion. After that, the second batch of equipment will be moved in," Liu Ning, chief engineer at the Ministry of Water Resources, was quoted as saying on CCTV.
The confirmed death toll of the quake was 67,183 on Tuesday, about 2,000 more than the confirmed count on Monday. Casualties are expected to hit 80,000.