MIANYANG, China Chinese officials rushed Tuesday to evacuate another 80,000 people in the path of potential floodwaters building up behind a quake-spawned dam as soldiers carved a channel to try to drain away the threat.
The official Xinhua News Agency reported emergency workers would try to complete the evacuation by midnight Tuesday, taking the number of people moved out of the threatened valley to almost 160,000, from more than 30 townships.
The Tangjiashan lake in northern Sichuan province, formed when a massive landslide blocked a river, is one of dozens of fragile dams created during the earthquake that pose a new destructive threat in the disaster zone.
Soldiers hauled explosives through the mountains to reach the area, and the official Chinese Daily said Tuesday on its Web site they were "preparing to dynamite the barrier." State television showed live footage of heavy earth-moving equipment being used to carve out a 200-yard channel to drain the water.
The lake is swelling behind a landslide near Beichuan, one of the towns hit hardest by the May 12 tremor that devastated Sichuan.
Residents of Huangshi village said they were told to move to a government-built tent camp on a hillside overlooking the river near Jiangyou town, southeast of Beichuan, to avoid the potential flood.
"We were told that so far it is the safest place for us to stay if the dam of the lake crashes," villager Liu Yuhua said Tuesday. "But we will have to move further uphill if the situation turns out to be worse."
The number of deaths from the quake has climbed further toward an expected toll of 80,000 or more. The Cabinet said Tuesday that 67,183 people were confirmed killed up by about 2,000 from a day earlier and 20,790 still were missing.
Elsewhere in the disaster zone, explosives were used to demolish some damaged buildings in the town of Yingxiu. Teams have been pulling down creaky buildings across Sichuan recently, using mostly excavators, bulldozers and other heavy machinery.
Aftershocks continued to rattle the region, including two temblors Tuesday afternoon that caused more than 420,000 houses to collapse in Qingchuan county, Xinhua reported. Additional details were not available about how the estimate was made. Phones were not answered late Tuesday at the Qingchuan county police department.
Sixty-three people were injured, including six who were critically hurt.
The U.S. Geological Survey measured a 5.2 magnitude aftershock that struck just after 4 p.m., followed by a magnitude 5.7 temblor about a half-hour later.
Dozens of aftershocks have further frayed survivors' nerves. A major temblor Sunday knocked down thousands of buildings that had survived the initial quake, and killed eight people.
One quake expert said that aftershocks in the area could continue for several months, though they would grow weaker as time passes.
"Judging from previous earthquakes of a similar magnitude, this time the aftershocks may last for two or three months," He Yongnian, a former deputy director of China Seismological Bureau, was quoted as saying by Xinhua.
Some 5 million people were left homeless by the quake, and many of them are living in tents or makeshift communities that are clustered throughout the disaster zone.
Qi Xiaoqiu, the director of disease prevention at the health ministry, said the quake had knocked out much of the region's health infrastructure, but 12 field hospitals had been put up and tens of thousands of health professionals were working in the zone.
"With the destruction by the quake, the living and sanitary conditions have worsened for the local population," Qi told reporters in Beijing. "Their physical conditions are weakened (and they are) more vulnerable to disease."
Diseases such as tuberculosis, hepatitis and diarrhea remained a threat, but so far no outbreaks had been reported, he said.
About 1,800 soldiers clambered up mountain paths to reach Tangjiashan with plans to dig and blast their way through the debris and drain the water, Xinhua reported. It did not say when the blasting operation would take place.
The Tangjiashan lake is the biggest of about 35 lakes created when the magnitude 7.9 quake sent millions of tons of earth and rock tumbling into some of the region's narrow valleys. Some rising floodwaters have already swallowed villages.
Tangjiashan now holds 34 billion gallons of water and was rising by more than three feet every 24 hours, Liu said.
Xinhua said troops blasted several tree trunks with explosives on Tuesday to help clear rubble and were working around the clock to remove at least 1.8 million cubic feet of debris to build the channel, which would not be completed before June 5.
Pressure is building behind the dams as rivers and streams feed into the newly formed lakes. Officials fear the loose soil and debris walls of the dams 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 two feet of rain that falls on the area each year.
Also in northern Sichuan in Qingchuan county, 1,300 people have been evacuated from Guanzhuang because of landslide worries. Local official Li Guoping said plans were being drawn up to evacuate all 23,000 people in the area if needed.
He said landslides that blocked rivers had formed 10 lakes, but only three had the potential to be dangerous if there were heavy rains.
"I worry about the start of the rainy season," Li said.