Soldiers forced to use anti-tank weapons to blast rock as quake lake threatens 1million people

Television and official Web sites showed People's Liberation Army troops firing 82 millimeter recoilless guns at debris on Sunday.

Troops dislodged enough debris to speed the drainage of waters in Tangjiashan lake, although the level continued to rise with the inflow from the blocked river behind the dam.

Another 120 troops were sent to continue the operations today.

Danger: A sluice channel that has been cut to release water from the Tangjiashan quake lake in Sichuan Province

Early Monday, the water level had reached more than 6ft above a spillway carved into the dam last week to divert water and release pressure on the unstable dam wall.

Authorities were on alert both for increased rainfall and new aftershocks that could weaken the dam or send more debris plunging into the lake.

David Petley, a geography professor at the University of Durham, warned the situation at the lake appeared to be reaching crisis levels.

"The teams on the dam are fighting a desperate battle now," Petley said. "The outcome is very uncertain."

Rising water levels indicate the outflow is not fast enough, he said.

Rescue operation: Chinese soldiers work on military trucks loaded with pontoon boats parked by a road

At the same time, news photos show that the top of the dam is holding, instead of eroding slowly as it should, while the channel further down was eroding too quickly.

That could place increased pressure on the dam by suddenly sucking down large volumes of water, overwhelming the barrier, Prof Petley added.

"I am increasingly concerned about the state of play as the level of the lake continues to rise and the channel at the crest of the dam does not appear to be eroding," he said.

New landslides sparked by a magnitude 5 aftershock on Sunday underscored the threat of flooding.

More than 250,000 people downstream have been evacuated in recent weeks, adding to the turmoil created by last month's massive earthquake in China's Sichuan province.

Threat: Engineers measure the drainage discharge in Tangjiashan.

Many were living in improvised camps on surrounding hillsides, surviving on instant noodles and suffering from heat, mosquitoes, and a lack of water for bathing.

The Tangjiashan lake was formed when rubble from a massive landslide set off by the deadly May 12 earthquake blocked the flow of the Tongkou River, also known as the Jianjiang.

Wooden houses, boulders and other debris have also been blasted to speed the flow of water into the spillway. Other troops have been deepening the channel and digging on a second spillway.

Managing the Tangjiashan lake has become a priority for a government working to head off another catastrophe even as it cares for millions left homeless after the 7.9 magnitude quake in Sichuan province.

More than 1.3 million people live downriver from Tangjiashan.

The death toll from the quake climbed Sunday to 69,136, with 17,686 people still missing.

The Tangjiashan lake is the largest of more than 30 created by last month's quake.

Government experts quoted by state media have played down the threat of imminent flooding, though a variety of factors could set off a dam collapse: rain, aftershocks, landslides and increased leakage from the barrier.