YINGXIU, China - A powerful aftershock knocked out roads and communications in some of the most earthquake-ravaged parts of central China yesterday as emergency crews rescued more than 30 people who had survived up to 100 hours trapped in the ruins.

With the official death toll from Monday's quake at more than 22,000, an air force unit reached Yinchanggou, a scenic spot in the mountains north of Chengdu, the capital of Sichuan province, and found that 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 were tourists, he said, without specifying whether they were foreign or Chinese.

Tens of thousands of people are believed buried or missing. There were about 12 million people living within a 60-mile radius of the epicenter, 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 that the government's response to China's worst disaster in 30 years could affect its image heading into the the August Olympic Games in Beijing, President Hu Jintao ramped up public-relations efforts, making his first trip to the stricken region.

In response to rising anger, government officials accustomed to tightly controlled media took the unusual step of fielding questions online about why thousands of schools that collapsed were not built to be quake-safe. Officials said they would investigate.

Damage from yesterday's magnitude-5.5 aftershock - one of dozens of strong tremors since the quake - 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 said.

The military-led recovery operation pushed farther into the remote corners of the disaster zone, with trucks navigating around boulders and splintered pavement that clogged roads into the forest-clad mountains of Beichuan county. Thirty-three survivors were pulled from the rubble of Beichuan's main city yesterday, Xinhua news agency said.

Still farther afield, soldiers slogged up a slippery mud path 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.

Augmenting the 130,000 soldiers and police deployed, specialized rescue teams from Japan, South Korea, Singapore and Russia arrived in the region and began work, Xinhua said. It was the first time China had accepted outside professionals for help in a domestic disaster.

Most buildings in Yingxiu collapsed in the quake and the rest appeared 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.

More than four million apartments and homes were damaged or destroyed in Sichuan.

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 . . . waiting," she said. "He's been missing for more than three days now. But for my son I would come every day."