The U.S. Geological Survey says it has detected a strong aftershock in China's earthquake-battered Sichuan province.

Thursday's aftershock registered a 5.3 magnitude, and was located 65 kilometers west of the town of Guangyuan.

The major project of a sluice from the Tangjiashan Lake is completed at quake-induced Tangjiashan Lake in southwest China's Sichuan province, 31 May 2008

The aftershock comes as Chinese officials have been sounding warnings about rising water levels of a so-called "quake lake" formed by last month's deadly earthquake.

The official Xinhua news agency reported Wednesday that Tangjiashan lake's waters will likely continue to rise over the next two days, as rainfall is expected through Friday. The agency says the lake is already close to overflowing.

Tangjiashan was created when landslides triggered by the May 12 earthquake blocked a nearby river. Soldiers dug a channel last week, hoping to drain the lake.

Xinhua says there is a plan to evacuate the lake, but does not specify how that plan will work.

Meanwhile, Chinese authorities are blocking access to schools destroyed by last month's earthquake in an apparent effort to quell demonstrations by angry, grieving parents.

Police and soldiers have been deployed outside several schools in Sichuan, where parents are demanding official accountability for what they say is the shoddy construction of the facilities. Notices have also been posted to remind the public to maintain social order.

Thousands of schools collapsed during the 7.9 magnitude earthquake and officials are growing increasingly anxious over public displays of anger and media coverage.

Officials have not said how many children died in the earthquake, but the death toll was raised again Wednesday to more than 69,100. Some 20,000 are still missing.

Some information for this report was provided by AP.