A magnitude six aftershock rattled the border between Sichuan and Gansu provinces in southwestern China Saturday, the same region hit by Monday's massive 7.9 magnitude earthquake.
There have been several aftershocks, including another one today which interrupted a speech by Chinese President Hu Jintao to rescue workers in the region.
Chinese authorities say that roads into the hardest hit areas had been reopened before the latest aftershock, making relief and recovery operations easier to carry out. Landslides set off by the original quake had blocked highways and forced rescue teams and supplies to be airdropped into the region.
China's official Xinhua news agency Saturday that landslides have blocked parts of the Qingzhu River, sparking fears that backed-up water will burst the banks and inundate the area.
Reporter Daniel Schearf was in the ruined city of Beichuan in Sichuan and saw hundreds of people running for higher ground. He said another journalist warned him to get to high ground fast.
The evacuation briefly hampered rescue efforts, but workers have returned to the area.
Authorities say the death toll is nearly 29,000. The number of dead is expected to surpass 50,000. Some five million people have lost their homes.
Xinhua says authorities in Beichuan County want to blow up part of the lake's embankment in an effort to relieve some of the water level pressure.
Officials fear many of the dead are children who were trapped when their schools collapsed during the earthquake. China's Housing Ministry has launched an investigation into the reason nearly seven thousand school buildings collapsed in the quake.
Supplies are short and China's health care system is struggling to cope with the nearly 160,000 people who are injured.
Foreign rescue teams are arriving in China to assist the 148,000 troops deployed in the affected areas.
Some information for this report provided by AP and Reuters.