CHENGDU, China -- One of the worst earthquakes to hit China in three decades killed nearly 10,000 people yesterday, trapped about 900 students, and caused a toxic chemical leak, state media reported.

The 7.9-magnitude earthquake devastated a hilly region of small cities and towns in central China. 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 city of Chongqing.

Xinhua said 80 percent of the buildings had collapsed in Sichuan province's Beichuan county, raising fears that 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.

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. The quake rumbled for nearly three minutes, witnesses said, driving people into the streets in panic.

While most buildings in the city held up, those in the countryside tumbled. On the outskirts of Chongqing city, a school in Liangping county collapsed, killing at least five people. Residents said teachers kept the children inside, thinking it was safer.

In Juyuan town, Xinhua said its reporters saw teenagers struggling to break loose from under the rubble of the three-story school. As many as 900 students were trapped and four ninth-graders were killed immediately, Xinhua said.

Landslides left most roads impassable, while heavy rains prevented four military helicopters from landing.

Mianyang city ordered all able-bodied males under age 50 to take water and tools and walk or drive to Beichuan, where most of the buildings had collapsed.

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 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.