CHONGQING, China — One of the worst earthquakes in decades struck central China on Monday, killing nearly 9,000 people, trapping about 900 students under the rubble of their school and causing a toxic chemical leak, state media reported.

The 7.8-magnitude earthquake devastated a hilly region of small cities and towns. The official Xinhua News Agency said 8,533 people died in Sichuan province and more than 200 others were killed in three other provinces and the mega-city of Chongqing.

Xinhua said 80 percent of the buildings had collapsed in Sichuan province's Beichuan county after the quake, raising fears the overall death toll could increase sharply.

State media said a chemical plant in Shifang city had cratered, burying hundreds of people and spilling more than 80 tons of toxic liquid ammonia from the site.

The earthquake sent thousands of people rushing out of buildings and into the streets hundreds of miles away in Beijing and Shanghai. The temblor was felt as far away as Vietnam and Thailand.

It posed a challenge to a government already grappling with discontent over high inflation and a widespread uprising among Tibetans in western China while trying to prepare for the Beijing Olympics this August.

The quake hit about 60 miles northwest of Chengdu — a city of 3.75 million — in the middle of the afternoon when classrooms and office towers were full. There were several smaller aftershocks, the U.S. Geological Survey said on its Web site.

About 1,200 pandas — 80 percent of the surviving wild population in China — live in several mountainous areas of Sichuan.

The earthquake hit one of the last homes of the giant panda at the Wolong Nature Reserve and panda breeding center, in Wenchuan county, which remained out of contact, Xinhua said.

The Wolong PandaCam, a live online video feed showing the activities of the pandas at the nature reserve, stopped showing footage of the animals late Sunday night.

The earthquake, China's deadliest since 1976, occurred in an area with numerous fault lines that have triggered destructive temblors before. A magnitude 7.5 earthquake in Diexi, Sichuan that hit on August 25, 1933 killed more than 9,300 people.

Xinhua said 50 bodies had been pulled from the debris of the school building in Juyuan town but did not say if the children were alive. Students also were buried under five other toppled schools in Deyang city, Xinhua reported.