Chinese state media say an aftershock has occurred at a lake formed by last month's earthquake and that the growing body of water is threatening to flood thousands of homes downstream.

Xinhua news says the aftershock of 4.8 magnitude struck the southwestern province of Sichuan Sunday, causing massive landslides on mountains surrounding the lake.

It says the aftershock's impact on the threatened area is under surveillance.

Earlier today, Xinhua said the lake is still rising "dangerously" despite efforts to drain the water safely.

Xinhua news agency quoted provincial official Zhang Ting as saying inflow is four-point-six times greater than outflow at the lake.

More than 1.3 million people live downstream from the lake, created when a quake-caused landslide formed a dam in the Tongkou river.  About 250,000 people have been evacuated from their homes.

The news agency said 600 police and soldiers have dug a channel to divert water from the lake, and that work on a second channel has begun.

Xinhua quotes Army General Ge Zhenfeng as saying construction of the drainage projects is going well, but that the lake remains dangerous for people downstream.

The general, who is supervising the drainage projects, says it will take a few days for the danger to be eliminated.

The 7.9 magnitude earthquake that hit Sichuan on May 12 killed more than 69,000 people.  Millions more were left homeless.