The modern world has never faced the threat of dangerous dams on anything like the scale of the crisis now unfolding in Sichuan in the aftermath of the earthquake two weeks ago, engineers say.

In addition to about 380 existing man-made dams that were significantly damaged by the 7.9-magnitude quake, the Chinese authorities are faced with an estimated 35 new "natural" dams formed when hills and mountains collapsed into rivers, according to the official Xinhua news agency.