Chinese residents try to salvage belongings from  collapsed building in Dujiangyan, in southwest China's Sichuan province, 13 May 2008

Chinese rescue workers are struggling to save the lives of thousands of people buried under collapsed buildings and schools across southwestern China's Sichuan province.

Official figures indicate Monday's 7.9 magnitude earthquake has left more than 12,000 people dead, and that toll is expected to rise.

The first rescue and relief troops arrived Tuesday at the epicenter of the quake in Wenchuan county, home to more than 100,000 people. An initial report from the official Xinhua news agency says soldiers confirmed the deaths of 500 people there, but a large number of people remain buried or missing.

Access to several of the major disaster areas is difficult, if not impossible, and information about the damage and casualties has been difficult to obtain.

Chinese rescuers evacuate an injured survivor from a collapsed buidling in Dujiangyan, southern Sichuan province, 13 May 2008

Xinhua reports that slightly more than 12,000 people have been killed, 9,400 buried and nearly 8,000 missing. However, a separate report by Xinhua says more than 18,000 people were buried in the city of Mianyang alone.

More than 50,000 troops have been sent to assist with relief work in quake-affected areas, but China has said conditions are not right for international teams to come in and help.

The United States says it will contribute $500,000 to China in earthquake relief aid. A cargo plane carrying 30 tons of Russian aid arrived Tuesday. Other countries have pledged assistance, and international aid agencies say they also are prepared to help.

U.S. President George Bush spoke with Chinese President Hu Jintao about the earthquake. Mr. Bush voiced his deep concern and said the United States is willing to provide any needed help.

Tibet's exiled spiritual leader, the Dalai Lama, also issued a statement expressing his deep sadness and offering prayers for those who died and were injured during the quake.