Rebuilding China's devastated towns and villages, to rehouse millions of people after the earthquake, could take three years.
Some towns in the earthquake zone in southwestern China will need to be relocated altogether because the terrain is not safe.
The known death toll from the quake already exceeds 55,000, but more bodies are expected to be found as the debris from the dozens of flattened cities, towns and villages is cleared.
More than 5.47 million people have been left homeless in southwestern Sichuan province.
The Beijing government is concerned that aftershocks and heavy rain could cause secondary disasters such as flashfloods and landslides.
So far, more than 7,000 aftershocks have been reported.
Relief workers are also concerned that poor hygiene could cause disease outbreaks.
Yesterday China ordered the immediate construction of 1m small homes to provide shelter to people left homeless by the 7.9-magnitude quake, which struck Sichuan province on 12 May.