Thousands of youths rampaged through Athens and the northern Greek city of Thessaloniki on Sunday, burning dozens of shops and vehicles in a second day of rioting after police shot dead a 15-year-old boy. Greece's worst protests in years erupted in the capital late on Saturday after the shooting of the teenager, and quickly spread to Thessaloniki and the tourist islands of Crete and Corfu. The conservative government, suffering a sharp drop in popularity in recent months, appealed for calm but leftist demonstrators and anarchists went on the rampage for a second day, staging running battles with security forces on Sunday. Police said more than 34 people had been injured, including one woman with a serious head wound, while 20 were detained. "We have briefed the Prime Minister," Interior Minister Prokopis Pavlopoulos, whose offer to resign was rejected, told reporters after a government meeting. "The rage is understandable but it cannot turn against all society." In recent years, anger among Greek youths has been fanned by the growing gap between rich and poor. Violence at student rallies and fire bomb attacks by anarchist groups are common. Prime Minister Costas Karamanlis, whose government has been shaken by scandals and an economic slowdown, pledged action in a public apology to the father of the dead boy. "I know nothing can relieve your pain, but I assure you ... the state will act, as it ought to, so that yesterday's tragedy won't be repeated," he said. In central Athens, glass, debris and charred cars were strewn across streets choked with tear gas. Few pedestrians ventured out, holding handkerchiefs to their faces. Residents in the bohemian district of Exarchia where the violence erupted left candles and flowers at the spot where police shot the boy, identified as Alexandros Grigoropoulos. "The whole neighborhood is smoldering, they even burned the post office," said resident Nefeli Chlideris, 25, a student. "Now we keep the windows shut because of the tear gas." For most of Sunday, protesters chanting "Killers in Uniform" rained petrol bombs down on rows of riot police while helicopters hovered overhead. More than 30 shops and a dozen banks were torched in the capital's busiest commercial districts ahead of the busy Christmas period. The mayor of Athens postponed the launch of Christmas festivities and vowed to help affected shopowners. As night fell, more than 1,000 students played a cat and mouse game with police. Police said they planned to pull out of the area overnight in order to defuse tensions.