These satellite images taken before, left, and after the May 12 earthquake in China were released by Taiwan's National Space Organization. A river pass near Beichuan, in China's Sichuan Province, has become blocked and the resulting lake now poses a flood hazard to people downstream.

Mianyang, China ? About 80,000 people were evacuated Tuesday downstream of an unstable earthquake-created dam that is threatening to collapse, and troops rushed to carve a trench to drain the water before it floods the valley.

The threat of flooding comes even as quake aftershocks continue to hit the region. Two temblors Tuesday collapsed hundreds of thousands of homes, the official Xinhua News Agency reported.

Dozens of lakes have been swelling behind walls of mud and rubble that have plugged narrow valleys in parts of the disaster zone, adding a new worry for millions of survivors.

More than 30 villages were emptied and the people were being sent to camps like one outside Jiangyou, where 12 to 15 people crammed into each of about 40 government-issued tents pitched on a hillside overlooking the river.

“We were told that so far it is the safest place for us to stay if the dam of the lake crashes,” said Liu Yuhua, whose village of Huangshi was one of those emptied. “But we will have to move farther uphill if the situation turns out to be worse.”

Xinhua said emergency workers labored into the night to try to get 80,000 people out. Another group of about 80,000 has already been moved out of the valley, it said.

Troops on Tuesday used explosives to blow up tree stumps that were hampering heavy-duty excavators that were airlifted by helicopter in recent days to the newly formed Tangjiashan lake near the decimated town of Beichuan, Xinhua said.

The magnitude-7.9 quake that struck Sichuan province May 12 sent a mass of dirt and rocks tumbling in the valley about two miles from the town in a spot not reached by roads, plugging a river that is now forming the lake.

The number of deaths from the quake climbed toward an expected toll of 80,000 or more. China’s Cabinet said Tuesday that 67,183 people were confirmed killed, with 20,790 still missing.