Draining of the dangerous Tangjiashan "quake lake" in Southwest China’s Sichuan province is continuing, but a high alert remains in place.

Army engineers have fired missiles to blast boulders in a man-made sluice channel to accelerate the draining.

The sluice channel was widened by three meters to about eight meters through missile blasting, to improve the flow of water.

Police and army staff were still working to widen the outlet with the help of bulldozers and excavators. The workers were also digging a second channel on the other side of the quake lake.

"Generally speaking, construction of the lake’s drainage projects goes on well, but the lake remains dangerous for hundreds of thousands of people downstream," said General Ge Zhenfeng, deputy chief of the General Staff of the People’s Liberation Army (PLA), who is supervising the relief work at the site.

"It will take us a few more days to eliminate the potential danger of the lake," he said.

About 600 armed police and the army’s engineering wing worked for six days to dig a 475-metre channel to divert water from the lake.

Rao Xiping, head of the Beichuan hydrometeorological station, told Xinhua the lake dam remained safe as the drainage continued.

"We found no obvious expansion of the sluice holes nor cracks on the dam. There is no sign of dam collapse either," said Rao, adding that the staff of his station and soldiers are keeping 24-hour watch along the dam.

Meanwhile, Water Resources Minister Chen Lei warned that increasing rainfall, aftershocks, landslides and leakage were still threatening the lake’s barrier.

Landslides on mountains near the lake are a threat, and they could pour another 17 million cubic metres of rocks and earth into the lake.

If that happens, the lake’s barrier would burst and workers on the barrier could be swept away, he said.

The Tangjiashan quake lake was formed after a massive quake-triggered landslide from Tangjiashan Mountain blocked the Tongkou River, which ran through the Beichuan county, one of the worst-hit areas in the quake.