BEIJING — A massive earthquake struck central China today and state media reported that as many as 5,000 people were killed in a single county while nearly 900 students were trapped under the rubble of their school.

The official Xinhua News Agency said 80 percent of the buildings had collapsed in Beichuan county in Sichuan province after the 7.8-magnitude quake.

Xinhua reported that 3,000 to 5,000 people had died in Beichuan, which has a population of 160,000, raising fears the overall death toll could increase sharply. Another 10,000 people were believed to be hurt.

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 Pakistan, Vietnam and Thailand.

Four of the dead were ninth-grade students killed when their high school collapsed, Xinhua said. Photos showed heavy cranes trying to remove rubble from the ruined school. Xinhua did not say how many of the students were feared dead.

It said its reporters in Juyuan township, about 60 miles from the epicenter, saw buried teenagers struggling to break loose from underneath the rubble of the three-story building "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 comes less than three months before the start of the Beijing Summer Olympics, when China hopes to use to showcase its rise in the world.

It struck in the middle of the afternoon when classes and office towers were full, about 60 miles northwest of Chengdu. There were several smaller aftershocks, the U.S. Geological Survey said on its Web site.

Calls into the city did not go through as panicked residents quickly overloaded the telephone system. The quake affected telephone and power networks, and even state media appeared to have few details of the disaster.

"In Chengdu, mobile telecommunication convertors have experienced jams and thousands of servers were out of service," said Sha Yuejia, deputy chief executive officer of China Mobile.