Its reporters saw 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."

Photos showed heavy cranes trying to remove rubble from the ruined school. Other photos posted on the Internet and found on the Chinese search engine Baidu showed arms and a torso sticking out of the rubble of the school as dozens of people worked to free them, using their hands to move concrete slabs.

Calls into the city did not go through as panicked residents quickly overloaded the telephone system and the quake also affected power networks.

Although it was difficult to telephone Chengdu, an Israeli student, Ronen Medzini, sent a text message to The Associated Press saying there were power and water outages there.

"Traffic jams, no running water, power outs, everyone sitting in the streets, patients evacuated from hospitals sitting outside and waiting," he said.

The road to Wenchuan from Chendu was cut off by landslides, state media said, slowing the rescue efforts.

Though news trickled out in the first hours after the quake, the government and its media quickly mobilized, with nearly 8,000 soldiers and police sent to the area. China Central Television ran non-stop coverage, with phone reports from reporters and a few isolated camera shots from the scene.

Disasters always pose a test to the communist government, whose mandate in part rests on providing relief to those in need. In recent years, the government has improved emergency planning and rapid response training for the military.

The earthquake also rattled buildings in Beijing, some 930 miles to the north, less than three months before the Chinese capital was expected to be full of hundreds of thousands of foreign visitors for the Summer Olympics.

Li Jiulin, a top engineer on the 91,000-seat National Stadium — known as the Bird's Nest and the jewel of the Olympics — was conducting an inspection at the venue when the quake occurred. He told reporters the building was designed to withstand a 8.0 quake.

"The Olympic venues were not affected by the earthquake," said Sun Weide, a spokesman for the Beijing organizing committee.

Skyscrapers swayed in Shanghai and in the Taiwanese capital of Taipei, 100 miles off the southeastern Chinese coast. There were no immediate reports of injuries or damage.

The quake was felt as far away as the Vietnamese capital of Hanoi, where some people hurried out of swaying office buildings and into the streets downtown. A building in the Thai capital of Bangkok also was evacuated after the quake was felt there.

A magnitude 7.8 earthquake is considered a major event, capable of causing widespread damage and injuries in populated areas.

The last serious earthquake in China was in 2003, when a 6.8-magnitude quake killed 268 people in Bachu county in the west of Xinjiang.

China's deadliest earthquake in modern history struck the northeastern city of Tangshan on July 28, 1976, killing 240,000 people.