Storms forecast for the region, meanwhile, added to concerns that rain would put more pressure on weakened dams and reservoirs and cause spillovers from new lakes that have built up behind debris from the earthquake.
The number of deaths from the quake climbed toward an expected final toll of 80,000 or more. The Cabinet said 65,080 people were confirmed killed, and 23,150 people remained missing.
Thousands of people had been evacuated from an area downstream from one of the new lakes that was created by a landslide near Beichuan, a town hit hard by the May 12 tremor that devastated Sichuan province.
Some 1,800 soldiers, each carrying 22 pounds of explosives, clambered up mountain paths to reach the new lake - already named Tangjiashan - with plans to blast through the debris and drain the water, the official Xinhua News Agency said. The troops didn't arrive until late Monday, and the blasting was not expected until Tuesday at the earliest.
The lake, fed by the Qingzhu River, lay two miles upstream from the center of Beichuan county.
With better weather allowing helicopter flights, heavy equipment was also delivered to the area to help remove debris, state media reported.
Tangjiashan lake is one of dozens caused when the magnitude-7.9 quake sent millions of tons of earth and rock tumbling into some of the region's narrow valleys. Rising waters have already swallowed some villages.
"The water was covering the road, and two days later I could not see the roof of my house anymore," said Liu Zhongfu, standing on a hillside looking down at another of the new lakes, which submerged the town of Shuangdian.
A sofa and bits of wood that were once part of houses could be seen floating among the debris in the milky green water. Villagers said they also had seen corpses in the water in recent days.
Liu, a 31-year-old truck driver, was working away from home when the earthquake hit, causing a landslide that cut the Chaping River in An county, about 30 miles south of Beichuan. His wife, 3-month-old daughter and 60-year-old mother escaped unhurt.
"I thought I could go back but I have nothing now. My village, it's all become a sea," he said. "I'm trying to see my house for one last memory."
Pressure is building behind the mounds of earth and rubble as rivers and streams feed into the newly formed lakes. Officials fear the walls of loose soil and debris could crumble easily, especially once the water level reaches the top and begins cascading over.
Adding to the threat, thunderstorms were forecast for parts of Sichuan this week - a foretaste of the coming summer rainy season that accounts for more than 70 percent of the 2 feet of rain that falls on the area each year.
The storms "could increase the risks posed by river blockages in some quake-hit areas," the China Meteorological Administration said .
In An county, the Chaping River backed up two miles along the valley, said Wang Li, county Communist Party secretary.
"We need to take care of this soon. This is a serious situation," he said.
The Water Resources Ministry said three small reservoirs in Shaanxi province, just north of Sichuan, were in danger of collapse after a strong aftershock Sunday - the latest of dozens that have rumbled across the region since May 12. A total 2,383 reservoirs were in danger across the country, the ministry said.
Elsewhere, 600 people were evacuated from Guanzhuang in Qingchuan county because of landslide worries.
"There's no danger for this exact moment from flooding but we are very worried because the whole mountain is loose," said Ma Jian, a local official.
At a meeting presided over by President Hu Jintao, China's top Communist Party leaders signed off on plans to shift the huge relief effort's focus from rescue to resettlement and reconstruction.
Survivors were plucked from crumbled buildings for more than a week after the quake, though the number of such tales has dwindled. Meanwhile, tent cities - some government organized, some makeshift - have sprouted across the disaster zone where 5 million people were left homeless.
In Qingchuan city, hundreds of survivors were living in a mix of lean-tos and government-provided tents in a public square. People crowded four or eight to a tent were being provided with packets of instant noodles and bottled water.
With each aftershock, survivors relive their horror at the quake two weeks ago.
"I was so scared, I didn't know where to run," said Deng Zuequin, 50, a vegetable seller, describing Sunday's shaking. "In my mind all things are connected to the earthquake. The earthquake takes up every inch of my mind."
Officials in Chengdu, the capital of Sichuan, said the country's one-child policy would be lifted for families that had a child killed, severely injured or disabled in the quake. Many of the dead from the disaster were children - although no specific numbers are known.
The Education Ministry said it would investigate whether flawed construction contributed to collapses of schools.
"We will punish those who cut corners during school building construction and will have zero tolerance for corruption and shoddy school projects," spokesman Wang Xuming said in Beijing.
Meanwhile, one of two pandas missing since the earthquake was recovered Monday, Xinhua said. The panda had been missing from the famed Wolong reserve, located near the epicenter.
