"We have made preparations to trigger underwater blasts, too, to make the channels deeper so that more water can flow out," Liu said.
But Water Resources Minister Chen Lei warned that heavy rainfall, aftershocks, landslides and leakage were still posing a threat to the dam.
A rainfall of 400-500 mm, well above the normal level, has been forecast for the upper reaches of Jianjiang River in June and July. That could cause water to overflow from the dam and even break it, causing flash floods.
Landslides could pour millions of cubic meters of rock and earth into the lake, which can be a real threat to the dam, he said.
The Tangjiashan quake lake is the largest of the more than 30 formed by landslides in Sichuan, and they pose a threat to 1.3 million people.
More than 250,000 people in low-lying areas of Mianyang city have been shifted to safer places, according to a plan that assumed a third of the lake's water could flow out after a breach in the dam.
About 1.2 million people have to be moved to safety if it's feared half of the water could flow out. And 1.3 million people need to be relocated if all the water flows out.
The country's industrial and mining sectors have lost 206.53 billion yuan ($29.5 billion) because of the quake, the State Council Information Office said yesterday.
Ministry of Industry and Information Technology figures show 4,003 big companies have resumed production, but 1,482 enterprises are yet to do so.
Xinhua