MIANYANG, China - Nearly 160,000 people have been evacuated downstream from 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 yesterday collapsed hundreds of thousands of homes, the official Xinhua News Agency reported.

Dozens of villages were emptied, the official China Daily said today. It quoted Premier Wen Jiabao as telling a meeting of the State Council, China's Cabinet, that handling the danger from the swelling lakes was the "most pressing task" right now.

The newspaper said 158,000 people had been evacuated in case the newly formed Tangjiashan lake bursts before soldiers and engineers can drain off water from it.

More than 30 villages were emptied and the people were being sent to camps like the one outside Jiangyou, where an Associated Press reporter saw 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 the last 80,000 people out.

Troops yesterday 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 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 above the town in a spot not reached by roads, plugging a river that is now forming the lake.

Elsewhere in the region, workers also used explosives to level some buildings that were left teetering by the quake - a further sign that officials have stopped rescue and recovery efforts in some places.

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

Aftershocks have been a steady threat, causing more damage and injuries and jangling the already-frayed nerves of survivors. The two yesterday caused more than 420,000 houses to collapse in Qingchuan county, Xinhua reported. Sixty-three people were injured, including six who were critically hurt.

The U.S. Geological Survey measured a magnitude-5.2 aftershock just after 4 p.m. (4 a.m. EDT) and one measuring 5.7 about a half-hour later.

In a live broadcast, state television showed heavy earth-moving equipment being used to carve a 200-yard channel to drain the water from the Tangjiashan lake.

At Tangjiashan lake, hundreds of troops were working around the clock to dig a channel that would divert the rising waters before they breach the top of the rubble wall. Officials fear the loose soil and debris wall could crumble easily if the water starts cascading over the top, and send a torrent flooding down into the valley.

The lake now holds 34 billion gallons of water and was rising by more than 3 feet every 24 hours, Xinhua reported.

Tangjiashan is the largest of some 35 lakes created by rubble blocking rivers in the quake zone. Some rising floodwaters have already swallowed villages, though only Tangjiashan was posing a risk of another big catastrophe.

Adding to the urgency, thunderstorms were forecast for parts of Sichuan this week - a foretaste of the summer rainy season that accounts for more than 70 percent of the 24 inches of rain that falls on the area each year.

Man-made dams in the mountainous region were also weakened by the quake, although officials said there is no major threat.

About 5 million people were left homeless by the quake, and many are living in tents or makeshift camps clustered throughout the disaster zone.

Mental Trauma Going Untreated

Across central China's

disaster zone, many earthquake survivors with mental trauma are going untreated because health services already are strained.

Hospitals and clinics

were destroyed in the quake along with so much else across Sichuan province, leaving acute shortages

of staff and facilities. Medical services have focused on treating crushed and broken bones, on amputated

limbs, and on preventing disease outbreaks.

No government estimate

of people needing psychological help has been released, although the state-run Legal Daily newspaper quoted an expert as saying the number could be as high as 600,000.

"China has been

struggling to help thousands of people distressed and traumatized" in the quake, the official Xinhua news agency said last week. "Many volunteers and experts have rushed to quake zones, but psychologists are still in great demand."

- Associated Press