A major earthquake measuring 7.8 on the Richter scale jolted Wenchuan County in southwest China's Sichuan Province at 2:28 p.m. on Monday, the State Seismological Bureau (SSB) said, revising its previous figure of 7.6.
The epicenter of the quake was located 31.0 degrees north latitude and 103.4 degrees east longitude, the bureau said.
Four pupils died in southwest China's Chongqing Municipality on Monday afternoon when an earthquake toppled two primary schools in the outer Liangping County of Chongqing.
More than 100 students were reportedly injured, the local government said.
With a population of 111,800, Wenchuan lies in the southeast part of the Tibetan-Qiang Autonomous Prefecture of Aba, 146 kilometers northwest of Chengdu, the provincial capital of Sichuan.
Wenchuan is home to the Wolong Nature Reserve, China's leading research and breeding base for endangered giant pandas.
Minutes later, at 2:35 p.m., an earthquake measuring 3.9 on the Richter scale jolted Tongzhou District in east Beijing. That quake's epicenter was 39.8 north latitude and 116.8 east longitude, according to the SSB.
The quake was also felt in Tianjin, about an hour's drive from Beijing, according to reporters from Xinhua's branch there.
Xinhua reporters in many other parts of China also reported tremors. Reporters in Chengdu said they saw cracks on the walls of some residential buildings in the downtown area, but no building collapsed.
Telecom networks in the cities of Chengdu, Chongqing and Zhengzhou paralyzed after the quake. People complained they were unable to complete calls on either fixed lines or cell phones.
Aftershocks were felt in Chengdu within hours after the earthquake. And cracks were seen in the walls of some buildings. Local radio in Chengdu quoted witnesses as saying that some houses collapsed in Dujiangyan.
The water fountain at Xinhua's Chengdu Bureau toppled, TVs and bookshelves rocked, and books and documents spread on the floor.
An underground water pipe was broken underneath a viaduct close to Chengdu's southern railway station, and the downtown Changshou Road was drowned. No emergency repairs vehicle has arrived by press time.
The mobile telecommunications network remains in failure in Chengdu and Chongqing Municipality.
Xinhua reporter Hai Mingwei said his apartment was in a mess, with the water pipe in the washing machine broken and water flooded the floor. "Bottles of drinks were also broken and the liquid was everywhere," he said. He and his parents escaped from home and joined crowds of people on the street.
When the quake hit, Hai said the ground became uneven. "For a moment I thought I was dizzy and dared not walk."
Many parts of China, even the remote southern island province of Hainan, and Bangkok of Thailand, felt the quake.
In Zhengzhou, capital of central Henan Province, people rushed out of homes and offices. Many said they felt dizzy and saw the ceiling light fixtures swinging back and forth.
The local government informed citizens with mobile phone messages about the earthquake. Schools told students to go home or gather them in the playground.
The airport expressway in Zhengzhou was closed after the earthquake.
In Lanzhou, capital of the northwestern Gansu Province, the quake set off alarms of many parked cars by the roadside.
Xinhua reporters in Yinchuan, capital of Ningxia Hui Autonomous Region, said they felt their office building rocking back and forth for about four minutes.
A retiree in Leshan City, Sichuan Province, said in a telephone interview that a wall in her garden had collapsed, while a repairman in Chongqing saw the ceiling of his factory crumble and raised the alarm among the staff, who quickly left the building.
In Shanghai, people were evacuated from office buildings in Hongqiao and Nanjing Road.
No casualties have been reported yet.
Maowen, a neighboring county of Wenchuan, was hit by an quake measuring 7.5 on the Richter scale in 1933, which claimed more than 9,000 lives. Songpan and Pingwu in the northwest of Sichuan Province were hit by an earthquake with a magnitude of 7.2 in 1976.
Chinese President Hu Jintao on Monday ordered all-out efforts to help those affected by the major earthquake. Premier Wen Jiabao was on his way to the area to direct the rescue work.
The Chengdu Military Area Command has dispatched troops to help with disaster relief work in the earthquake-stricken area, military sources said.