An unstable lake created by a landslide is China's "most urgent task" in the aftermath of this month's massive earthquake, Vice Premier Hui Liangyu said, according to state-run media.

Tons of earth-moving equipment and explosives have been flown to the site of the quake-created dam in southwestern China's Beichuan county. Engineers are attempting to create a spillway to relieve water pressure as the Jianjiang River fills in behind the massive pile of rock and soil.

"The Tangjiashan quake lake should be our most urgent task," Hui said. "It is threatening millions of lives in the area downstream and any negligence will cause new disasters to people who have already suffered the quake."

Authorities have evacuated 158,000 people from nearly 170 communities, but that number could swell to 1.3 million if engineers become convinced a catastrophic release of water is about to occur, the Xinhua news agency reported.

The so-called quake lake is holding 170 million cubic yards (130 million cubic meters) of water and it has risen to within 83 feet (25) meters of the top of the dam.

The volume of water is equal to about 50,000 Olympic-size swimming pools, according to Liu Ning, chief engineer of the Ministry of Water Resources.

Creating a spillway to relieve the pressure is expected to take 10 days, state media reported, allowing enough time if the lake continues to rise at its average of about 6 feet (2 meters) per day.