Deputy Water Resources Minister Jiao Yong told a news conference in Beijing that though work to drain the lakes had largely been successful, there was still a threat to hundreds of thousands of people living downstream.

"Although disaster relief efforts have achieved a major initial victory, the flood situation in the disaster area is much more severe than in previous years," he said.

"Rainfall is expected to be much higher than in previous years during the flood season, and there may be large floods," Jiao added.

The government sent hundreds of soldiers, armed with explosives and heavy lifting equipment, to clear the blocked rivers, and evacuated residents downstream, causing further misery for people whose houses were destroyed in the quake.

Jiao cautioned that people could still be in danger.

"The quake lakes which are no longer in danger have yet to go through the experience of large floods. Heavy rain and aftershocks may induce rockslides that lead to more quake lakes," he said. (Reporting by Ben Blanchard; Editing by Jerry Norton)