Mu Lai Chao watched the building collapse on her son.
In an instant the ground had shaken and the smooth walls had buckled and now there were only piles of concrete trapping hundreds of schoolchildren. Her husband ran to the rubble, pulling the injured out.
"He saw them buried," she told ABC News in Chongqing. "One was bleeding heavily from the leg."
Her son survived but four of his classmates were killed, part of the deadly toll from China's worst natural disaster in three decades, a three-minute-long, magnitude 7.9 earthquake that struck China's most populous province Monday afternoon.
The horrific dimensions of the destruction and loss of life continued to grow as rescuers clawed through demolished towns and cities only to find heartbreak and misery.
The death toll in Sichuan Province alone has topped 12,000, with an additional 18,645 still buried in the rubble of the city of Mianyang, the official Xinhua News Agency reported today.
State TV quoted He Biao, director of the emergency office in the Aba region, saying that soldiers who marched to the town of Yinxiu believe that only 2,300 of the town's 9,000 people survived.
The killer quake arrived when schools and other public buildings were packed, leaving many schoolchildren among those buried in the flattened buildings.
Government rescue workers today finally reached Wenchuan county, the epicenter of the earthquake, only after hiking through rugged terrain. Heavy rain and roads studded with boulders have hampered the search effort.
More than 30,000 troops are deployed by the government in and around the epicenter, which is located in the country's teeming Sichuan province.
It is home to one out of every 50 people on the planet, with many villages hard to reach, lodged in the mountains where roads are easily blocked and helicopters could not land today because of the bad weather.
About 300 aftershocks have rattled the region since the earthquake, including a handful that measured between magnitude 4 and 6 today. People have been sleeping in tents, afraid to return to their homes, making the massive task of rescue workers all that much harder.
"The situation is worse than we previously estimated," Chinese Prime Minister Wen Jiabao told aid workers in Dujiangyan, a city 45 miles from the epicenter, according to Xinhua, the official news agency. "At present, we have great difficulties carrying out our rescue work."
In Dujiangyan, television images show a town that looks like it was hit by an airstrike. Bodies dug from the rubble are being lined up on the road. The air is filled with sirens and dust. Rescue teams have been trying to reach a woman who is eight months pregnant, trapped beneath a seven-story apartment building.
At least eight schools in Sichuan province literally crumbled when the earthquake hit. At one school, fewer than 100 of 420 students survived, Xinhua reported.
In Juyuan, 60 miles from the epicenter, a three-story middle school collapsed into a pile of rubble 5 feet high, burying as many as 900 students.
"Some had jumped out of the window and a few others ran down the stairs that did not collapse," a teacher told Xinhua. Cranes have been brought in, but there is no power. The town's hospital was also destroyed in the earthquake. The bodies of 50 dead children have been taken out of the rubble.
Zhou Chun told The Associated Press, "My wife died in the quake. My house was destroyed." He walked out of Dujiangyan with a wet blue blanket draped over his shoulders. "I am going to Chengdu," he said, "but I don't know where I'll live."
In Wenchuan, the local communist party secretary told Xinhua that at least 30,000 of the county's 105,000 residents slept outside Monday night.
In Beichuan county, 30 miles away, 80 percent of the buildings fell and 10,000 people were injured.
"People were just outside running around, crying, there were people running around, blood coming off of them," Heather Rauch, a junior at Texas A&M who was visiting Changdu, told ABC's "Good Morning America."
"You could look up at buildings and there were giant cracks running from the bottom all the way to the top of the buildings," she said.
She walked to a hospital that was being evacuated.
"We saw people who looked like they were on their death bed and they were being carried out," she said. "You looked at these people's faces and you just knew they had no idea what had just happened."
Lucy Jones, chief scientist for the Multi Hazards Demonstration Project at the U.S. Geological Survey, said the earthquake happened on the Longmenshan Fault, which is pushing the Tibetan Highlands up and over the Sichuan Basin.
"This fault was recognized as one of [the] dangerous faults of China," Jones told "GMA."
"Given the size and the location of this earthquake, we've only touched [the] surface of damage in Sichuan," she said.
Jones said a quake of this magnitude will instantly turn a brick building into a rubble.
"When you shake brick, the mortar in between dissolves. The building comes down and the roof kills people. They're some of the most deadly buildings in the world," she said.
A magnitude 7.9 quake can turn ground with a sandy base into quicksand, toppling buildings sideways as if they were bobbing on water, a phenomenon known as liquefaction, Jones said.
From what she knew of the area, "It's probably going to be sandy and probably subject to liquefaction."
China has launched a massive and unprecedented aid effort. In Mianyang, all able-bodied males younger than 50 years old were ordered to take water and tools and walk or drive to Beichuan. The government announced a national drive for blood donors. State airlines were asked to transport aid. And the Red Cross society of China called for donations. The government says it welcomes aid but is not allowing foreign relief workers into the area around the epicenter.
"Not one minute can be wasted," the Chinese prime minister, a geologist by training, said. "One minute, one second could mean a child's life."
But not everyone in need has been reached, and hope in pulling bodies out of the rubble is decreasing. Only 58 people have been extracted out of buildings, Xinhua reported.
"Time is of the essence," Wang Zhenyao, the disaster relief division director at the Ministry of Civil Affairs, told reporters in Beijing. Rescue efforts, he said, could take up to a week. "Survivors can hold on for some time. Now it's not time to give up."
With the Olympics now only three months away, officials are aware that failure to deal humanely and efficiently with this quake will be a public relations disaster. They are also anxious to avoid the reputation of bureaucratic indifference that has marked Myanmar's cyclone relief efforts.
To head off any suspicion that China wasn't making a massive relief effort, the prime minister was shown on Chinese television amid the quake's debris directing rescue efforts with a bullhorn in hand.
"Hang on, the army is here to rescue you," he said to those trapped under buildings.
When the ground started shaking beneath their feet, teachers at the Wenhua Township Primary School in Chongqing first told the kids to wait where they were, but eventually told them to run. As they did, the school collapsed.
Those who survived were treated in the open outside the city's hospital. Doctors feared that the hospital could collapse from another aftershock.
"My daughter lost her right arm," one woman told ABC News.
"I feel," she said, "like the sky has fallen on me."
Linda Owens contributed to this report