Chinese troops racing to drain an "earthquake lake" made substantial progress digging a diversion channel and have created emergency escape paths in case a mud and rock dam gives way.

The landslide-blocked river at Tangjiashan in southwest China is now the most pressing danger after an earthquake devastated the region on May 12.

Meanwhile, an official investigator pinpointed the poor design and construction of at least one of the many schools that collapsed during the 7.9 magnitude quake, killing thousands of children.