A strong aftershock sparked landslides Friday near the epicenter of this week's powerful earthquake, as the official death toll from the disaster rose above 22,000. The landslide buried vehicles and again cut off ravaged areas of central China. Across the disaster area, survivors were still being found alive after being buried in rubble for four days, and the first foreign rescue workers were allowed to the scene. Public anger erupted over the hundreds of children crushed to death in schools that collapsed in Monday's magnitude 7.9 temblor. An aftershock rattled parts of central Sichuan province Friday afternoon, the official Xinhua News Agency said, citing its reporters at the scene. A number of vehicles were buried on a road leading to the epicenter, and casualties were unknown. The US Geological Survey said the latest tremor measured magnitude 5.5 and was centered 6.2 miles below the surface, a relatively shallow quake, like the initial disaster. Education and housing officials took the rare move of fielding questions online from angry Chinese citizens over the many children among the official death toll, which the government said Friday had risen to about 22,069. Another 14,000 were still buried in Sichuan. The government said it would investigate why so many school buildings collapsed in the quake - destroying about 6,900 classrooms, not including the hardest-hit counties - and severely punish anyone responsible for shoddy construction. More than 4 million apartments and homes had been damaged or destroyed in Sichuan province, according to Housing Minister Jiang Weixin, and officials have said they expect the earthquake will eventually claim more than 50,000 lives. A day past what experts call the critical three-day window for finding buried survivors alive, rescuers pulled a nurse to safety who had been trapped for 96 hours in the debris of a clinic in Beichuan county, one of 17 people saved there, Xinhua reported. Survivors were also being found elsewhere, with a man pulled from the wreckage of a fertilizer plant near Shifang city. As rescuers moved into the epicenter, police restricted the last couple kilometers of road into Beichuan to emergency vehicles. Military trucks and cranes edged around huge fallen boulders. Dozens of people trudged up the winding mountain road, carrying backpacks and bags with food and medical supplies, on a quest for missing relatives. Liu Jingyong, a 43-year-old migrant worker searching for his cousin, traveled two days by bus and now foot just to get near his relative's home. "I have not had any information from him," Liu said. "This is so hard on me." One villager, Pan Guihui, stood on the side of the road with a vacant look on her face. She and her husband had just hiked 13 hours with her 1-year-old child, father and two brothers away from their destroyed village further up the mountain. They had stayed in the rubble until rescue workers arrived and ordered them out because of fears of landslides. "I have just been so frightened this whole time. I don't know what we are going to do," said Pan, 35. The only belongings the family had were some clothes and a little food, among hundreds camped along the road. "We've lost everything. There's nothing left of our village, nothing left of our home." As she spoke, hundreds of soldiers marched by in long columns out of Beichuan, some carrying shovels. In the city of Hanwang, Zhou Furen walked hours by foot - borrowing the army green shoes she was wearing - to a factory where her son had worked and remained missing. "I've been coming here every day, sitting here in the early morning, waiting," she said, weeping. "He's been missing for more than three days now. But for my son I would come every day." President Hu Jintao made his first trip to the disaster zone, rallying troops among the massive relief operation of some 130,000 soldiers and police. "The challenge is still severe, the task is still arduous and the time is pressing," Hu was quoted as saying by Xinhua. "Quake relief work has entered into the most crucial phase. We must make every effort, race against time and overcome all difficulties to achieve the final victory of the relief efforts." The first international relief crews arrived in the disaster zone, with Japanese rescuers starting work. China initially was reluctant to accept foreign offers of help, but the Foreign Ministry said Friday that specialist teams from Russia, South Korea and Singapore were also welcome. It was the first time ever that China accepted outside professionals for domestic disaster relief, Foreign Ministry counselor Li Wenliang told Xinhua. The government said it had allocated a total 5.4 billion yuan ($772 million) for earthquake relief, according to the central bank's Web site, up sharply from 1.11 billion yuan two days ago. Given the widespread destruction, AIR Worldwide - a catastrophe risk modeling firm - estimated losses to both insured and uninsured property would likely exceed $20 billion.