Much of the area has been closed to foreign media and travelers since then, compounding the difficulties of getting information. Roads north from Chengdu to the disaster area were sealed off early Tuesday to all but emergency convoys.

In Chengdu, the region's commercial center, the airport closed for seven hours, reopening only for emergency and a few outbound flights. A major railway line to the northeast was ruptured, stranding about 10,000 passengers, Xinhua said. Although most of the power had been restored by nightfall, phone and Internet service was spotty and some neighborhoods remained without power and water.

Nervous residents spent the night outside, some playing cards or heading to the suburbs. State media, citing the Sichuan seismology bureau, reported 313 aftershocks.

"Traffic jams, no running water, power outs, everyone sitting in the streets, patients evacuated from hospitals sitting outside and waiting," said Ronen Medzini, an Israeli student in Chengdu, via text message.

When it hit shortly before 2:30 p.m., the quake rumbled for nearly three minutes, witnesses said, driving people into the streets in panic.

"It was really scary to be on the 26th floor in something like that," said Tom Weller, a 49-year-old American oil and gas consultant staying at the Holiday Inn. "You had to hold on to something like that or you'd fall over. It shook for so long and so violently, you wondered how long the building would be able to stand this."

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

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

State TV broadcast tips for anyone trapped in the earthquake. "If you're buried, keep calm and conserve your energy. Seek water and food, and wait patiently for rescue," CCTV said.

China's two stock exchanges suspended trading Tuesday in 66 companies based in the region in an effort to minimize potential disruptions from the disaster. In Tokyo, Toyota Motor Corp. spokesman Toshiaki Hori said production had been suspended at the company's Chengdu factory.

Although initially measured at 7.8 magnitude, the U.S. Geological Survey later revised its assessment of the quake to 7.9. Its depth — about six miles below the surface, according to the USGS — gave the tremor such wide impact, geologists said.

The earthquake also rattled buildings in Beijing, 930 miles to the north, causing evacuations of office towers. People ran screaming into the streets in other cities, where many residents said they had never felt an earthquake.

In Beijing, where hundreds of thousands of foreign visitors are expected for the Olympics, stadiums, arenas and other venues for the games were undamaged.

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 a site inspection when the quake struck. 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. "We considered earthquakes when building those venues."