A powerful aftershock knocked out roads and communications in some of the most quake-ravaged parts of central China on Friday, as emergency crews rescued 163 people who had survived up to 100 improbable hours trapped in the ruins.

As Saturday dawned, rescuers were holding out hope of finding more survivors and authorities were preparing for the daunting task of housing and feeding millions left homeless.

With the official death toll at more than 22,000, an air force unit reached Yinchanggou, a scenic spot in the mountains north of the Sichuan provincial capital of Chengdu, finding landslides had swept away rustic small hotels.

"There are several hundred hotels, including farmer homestays, probably 800 in all. They are all rubble now," Cai Weisu, an official with an air force unit from the Chengdu Military Region, told Sichuan Television. Most of the dead are tourists, he said, but did not identify whether they were foreign or Chinese.

Tens of thousands of people are considered buried or missing throughout the disaster zone. There were about 12 million people living within a 60-mile radius of the epicenter of Wenchuan, according to a study on the potential impact of the quake by Xu Mingbao, a senior researcher at the University of Michigan's China Data Center.

Acutely aware its response to China's worst disaster in 30 years could affect Beijing's image heading into the Olympic Games, President Hu Jintao ramped up the government's public relations efforts, making his first trip to the stricken region.

And in response to swelling anger, government officials accustomed to tightly controlled media took the unusual step of fielding questions from people online about why thousands of schools that collapsed were not built to be quake-safe.

Damage from the magnitude-5.5 aftershock _ one of dozens of strong tremors since the devastating quake Monday _ was a temporary setback to the mammoth relief operation. Repair crews were rapidly restoring mobile phone services and unblocking roads within four hours, state media reported.

Trucks navigated around boulders and splintered pavement that clogged roads into the forest-clad mountains of Beichuan county, about 100 miles north of Chengdu.

China Central Television reported Saturday that rescue teams in the earthquake zone pulled 163 people alive from the rubble on Friday.

Augmenting the 130,000 soldiers and police deployed, the official Xinhua news service said specialized international teams had joined the effort_ the first time ever that China has accepted outside professionals for help in a domestic disaster.

On Saturday, teams from South Korea, Singapore and Russia joined a Japanese specialist group.

Meanwhile, a U.S. Air Force cargo plane loaded with tents, lanterns and 15,000 meals left Hawaii Saturday for China. It is the first aid flight from the United States to help in Sichuan province. Another Air Force delivery was due to go to China from Alaska.

In one hard hit area, soldiers slogged up a slippery mud path Friday into the village of Yingxiu, as some of their comrades stayed back and used rubble from landslides to patch the road so supply and rescue vehicles could get closer.

Most buildings in the village collapsed in the quake and the rest appear damaged beyond repair. Hundreds of residents huddled in tents. Small groups of soldiers, some lugging body bags, rushed from place to place checking reports of people trapped. They pulled out bodies and _ at least twice _ survivors. Others dug a burial pit and laid in at least 80 bodies.

Helicopters whirred overhead, bringing supplies and dropping leaflets with survival instructions that included not drinking dirty water and staying away from collapsed buildings. "We should trust the party and the government," the leaflets also said.

The government said it would investigate why so many school buildings collapsed in the quake and severely punish anyone responsible for shoddy construction. Officials in at least six provinces promised to tear down dangerous school buildings to protect students, state media reported. The quake destroyed about 6,900 classrooms, not including those in the hardest-hit counties.

China's education system is chronically underfunded. Building experts said the problem here, as in many other parts of the world, was a lack of commitment by governments to improve the quality of school buildings.

"Schools should never collapse, and hospitals and fire stations should never collapse. These are all civic structures that are needed in a disaster," said Roger Bilham, a professor of geological sciences at the University of Colorado at Boulder. "So when I hear a school has collapsed, I point the finger at politics."

More than 4 million apartments and homes were damaged or destroyed in Sichuan, Housing Minister Jiang Weixin told reporters.

Worried relatives went to sites where missing loved ones might be.

In the city of Hanwang, Zhou Furen walked for hours in borrowed shoes to a factory where her son had worked.

"I've been coming here every day, sitting here in the early morning, waiting," she wept. "He's been missing for more than three days now. But for my son I would come every day."

The government said it had allocated $772 million for earthquake relief, according to the central bank's Web site, nearly five times the amount two days earlier.

China has also received $457 million in donated money and goods for rescue efforts, according to the Ministry of Civil Affairs.

AIR Worldwide _ a catastrophe risk modeling firm _ estimated losses to both insured and uninsured property would likely exceed $20 billion.

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Associated Press writers Audra Ang in Beichuan, Tini Tran in Hanwang and Cara Anna in Beijing contributed to this report.