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.

Tangjiashan quake lake
In this photo released by China's Xinhua News Agency, the Tangjiashan quake lake formed by the landslide following the May 12 earthquake near Beichuan County in southwest China's Sichuan Province is seen on Monday, May 26, 2008. 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.

"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 lake is swelling behind a landslide near Beichuan, one of the towns hit hardest by the May 12 tremor that devastated Sichuan.

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.

Also Tuesday, an aftershock measured by the U.S. Geological Survey at magnitude 5.7 rumbled across the region, and Xinhua reported it had injured five people, without giving details.

It was the latest of dozens of aftershocks that 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 one of dozens 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 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.