Hussein Hamada, a 23-year-old medical student from the upper Galilee, was still missing on Tuesday night a day after a powerful earthquake struck central Italy, killing at least 207 people and injuring 1,500. Relatives of the missing waited in agony as rescuers dug desperately by hand for survivors, jarred by a strong aftershock that drove home the continuing danger in the historic city of L'Aquila. Tent camps housed some of the 17,000 left homeless by Italy's worst earthquake in three decades, but many spent the night in the chill mountain air without blankets or covers. Officials said some 10,000 to 15,000 buildings were either damaged or destroyed; teams planned to begin surveying those buildings still standing on Wednesday to see if residents could move back in. Aerial footage showed the scale of the destruction in this city of Romanesque, Gothic, Baroque and Renaissance architectural treasures. Roofs were missing from modern buildings, old churches had fallen walls and parts of medieval buildings had tumbled to the ground. Rescuers located four students trapped inside a partially collapsed dormitory Tuesday afternoon. Tearful emergency workers declined to say whether they were alive or dead, telling reporters that doctors would have to announce that. "Unless there is a miracle, I've been told (by rescuers) that they probably are dead," L'Aquila University rector Ferdinando Di Orio said. Chief firefighter Sergio Basti ordered the area evacuated so rescue crews could "surgically" remove big chunks of fallen masonry since the four were in a hard-to-reach spot and the building was so unstable. Firefighters briefed relatives of the victims on the rescue effort, explaining that civilians had to leave the scene for security reasons. The ANSA news agency said a 24-year-old student, Marta Valente, was pulled alive with the help of expert cave explorers, from the rubble of a four-story building in L'Aquila more than 22 hours after the quake. Premier Silvio Berlusconi surveyed the devastated region by helicopter and said the rescue efforts would continue for two more days - "until it is certain that there is no one else alive." He said some 15 people were still missing. Berlusconi said that at least 100 of the roughly 1,000 injured people were in serious condition. Rescuers ran from the rubble of the four-story dormitory when the 4.9-magnitude aftershock hit at 11:26 a.m., the latest in a series of aftershocks that hit L'Aquila and 26 surrounding towns and cities in the snowcapped Apennine mountains. The aftershock appeared strongest around L'Aquila, a city of some 70,000 people. Two buildings in the suburb of Pettino collapsed following the aftershock, the news agency ANSA reported, citing fire officials. No one was believed to be inside either building. The ground shook in the nearly town of Onna, about six miles away, but caused no panic. Residents walked around dazed, clutching whatever heirlooms they had managed to grab from their homes before they collapsed. "We lost 15 members of our family. Babies and children died," 70-year-old retiree Virgilio Colajanni said as he choked back tears. Onna had about 300 residents and lost 38 to the quake. Civil protection Maj. Cristina DiTommaso, who was helping coordinate the rescue in Onna, said search efforts were complicated by the fact that there were an unknown number of undocumented immigrants there. Rescuers were still trying to reach more isolated hamlets on Tuesday. While the elderly, children and pregnant women were given priority at tent camps in the area, others were sleeping in cars or making arrangements to stay with relatives or in second homes out of the quake zone. Ines D'Alessandro, 98, moved to her sister's home in nearby Sulmona after surviving her second devastating quake. Her first - a 1915 temblor which killed 30,000 people - occurred when she was just four years old, ANSA said. "It is hard. I cry my heart out for all of these people struck by this tragedy, but one needs to have courage and I try to give it to others. I have fought all of my life," D'Alessandro told ANSA. Six months pregnant, Sandra Padil spent the night in a tent without any covers in the chill mountain air as the temperatures dipped to 6 Celsius (43 Fahrenheit). "We are calmer out in the open," said Padil, a 32-year-old Peruvian who has been living in L'Aquila since 1996. "We didn't have blankets and it was cold, but at least this morning they gave us breakfast. Let's hope this ends quickly." Some elderly people appeared to be disoriented as they walked among the tents, and people tending them complained about the lack of blankets. Mounting piles of rubble contained torn clothing, ripped stuffed animals and broken furniture. The U.S. Geological Survey said the main quake - which struck just after 3:30 a.m. Monday - was magnitude 6.3 on the so-called "moment scale," but Italy's National Institute of Geophysics, using the Richter scale, put it at 5.8. Rescue workers arrived from throughout Italy, from as far away as Venice and Genoa. Part of L'Aquila's main hospital was evacuated for fear of collapse, and few operating rooms were in use. Law-enforcement cordoned off the areas hardest hit by the quake to prevent looting, including the center of L'Aquila and the towns of Paganica and Onna, Capt. Ivan Centomani of Italy's financial police told Sky Italia TV from L'Aquila. Italy's national police chief, Antonio Manganelli, said several people had been arrested for looting from abandoned houses. The quake took a severe toll on L'Aquila's prized architectural heritage. Many landmarks were damaged, including part of the red-and-white stone basilica of Santa Maria di Collemaggio. The bell tower of the 16th-century San Bernardino church and the cupola of the Baroque Sant'Agostino church also fell, the Culture Ministry said. Stones tumbled down from the city's cathedral, which was rebuilt after a 1703 earthquake. Damage to monuments was reported as far away as Rome, where cracks appeared at the thermal baths built in the 3rd century by the emperor Caracalla, Culture Ministry official Giuseppe Proietti said. Berlusconi declared a state of emergency, freeing up millions in euros to deal with the disaster, and canceled a visit to Russia so he could deal with the crisis. Condolences poured in from around the world. President Barack Obama phoned Berlusconi to offer sympathies as well as assistance if it was needed, the State Department said. It was Italy's deadliest quake since Nov. 23, 1980, when a 6.9-magnitude quake hit southern regions, leveling villages and causing some 3,000 deaths. The last major quake to hit central Italy was a 5.4-magnitude temblor that struck the south-central Molise region on Oct. 31, 2002, killing 28 people, of which 27 were children who died when their school collapsed.