CHONGQING, China -- Teenagers could be heard screaming for help from beneath school building rubble after a massive earthquake struck central China on Monday. At least 8,500 people are reported dead, and the toll is expected to rise.

Camera Catches China Quake | CNN Coverage

Close to 900 students were reported trapped underneath collapsed school buildings in one province.

The official Xinhua news agency 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.

Xinhua News Agency said 8,533 people died in Sichuan, and dozens of other deaths were reported elsewhere.

The news agency said that another 10,000 people were believed hurt in one of the Sichuan province's counties.

Xinhua reporters reported seeing buried teenagers struggling to break loose from underneath the rubble of the three-story building in Juyuan "while others were crying out for help." Two girls were quoted by Xinhua as saying they escaped because they had "run faster than others."

The earthquake -- upgraded to a 7.9-magnitude from a 7.8-magnitude -- also caused ammonia to be spilled from a chemical plant.

The quake was among the worst to strike China in decades, devastating a hilly region of small cities and towns in Sichuan and nearby provinces.

The news agency said the quake collapsed 80 percent of the buildings in Sichuan province, including a school where the students are trapped.

The quake was centered about 60 miles northwest of Chengdu, but it sent thousands of people rushing out of buildings and into the streets of Beijing and Shanghai, hundreds of miles away.

It struck at 2:28 p.m., when schools and office towers were full.

The rumbling was also felt in Taiwan, Vietnam, Thailand and Pakistan.

There have been several aftershocks.

One person in a town near the quake's epicenter said there are traffic jams and no running water. Power is out and phone lines are jammed.

State television broadcasted tips for anyone who is trapped, telling them: "Keep calm and conserve your energy. Seek water and food, and wait patiently for rescue."

Local officials near the epicenter of the quake said buildings cracked and collapsed and mountain roads were damaged.

Chinese Premier Wen Jiabao was heading to the area.

In the Vietnamese capital of Hanoi, some people hurried out of swaying office buildings and into the streets downtown.

A witness reached by phone in Chengdu said people flooded from buildings, but there were no reports of damage or injuries there.

The quake also was felt in the Taiwanese capital of Taipei, 100 miles off the southeastern Chinese coast.