Athens - Civil unrest over the weekend shooting of a teenager by police continued early Monday across Greece as hooded youths clashed with riot police for a second straight day.

Two days of rioting left Athens and the northern port city of Thessaloniki resembling war zones as self-styled anarchists torched cars, banks, police precincts, car dealerships, government buildings, private homes and stores and erected blazing barricades.

Despite charges of manslaughter filed against two of the police officers allegedly involved in the shooting, the violence continued unabated.

Entire streets and avenues remained blocked by burned and overturned vehicles, and garbage bins and tear gas filled the air throughout Athens and Thessaloniki.

Hundreds of students taking part in the riots have sought shelter in the Polytechnic and Economic Universities, which is off limits to police under Greek law, reports said. The Polytechnic university was the scene of a major student uprising during the military dictatorship that ruled Greece from 1967-74.

Early Monday, some 150 hooded youths who had sought shelter inside the Polytechnic University were reportedly still battling riot police outside the school gates, throwing stones and fire bombs.

Riot police, apparently having run out of tear gas following two days of protests, were retaliating by throwing stones at the youths.

Television reports said that a bookstore near the university was set ablaze in early Monday, and firefighters rushed to the scene to extinguish the flames.

Prime Minister Costas Karamanlis, whose government has been under pressure recently following a spate of scandals, promised a full investigation into events leading to the teenager's death.

With violence in full force across Greece, he called an emergency meeting of interior and public order ministers late Sunday in an effort to find a solution.

The rioting and protests began late Saturday in Athens, shortly after the shooting in the central district of Exarchia.

The exact circumstances are still unclear surrounding the shooting of the teenager - whose age was reported in varying accounts as either 15 or 16. Police said the shooting occurred after groups of youths began attacking a police car with stones and firebombs.

A purported warning shot by a police officer inflicted a serious stomach wound to the teenager, who died on arrival at a hospital.

Witnesses claim that there was only a verbal exchange between the youths and police, and that the police officer shot fired into the group.

"It was cold-blooded murder," an eyewitness told a radio broadcaster.

On Sunday, thousands of people in both cities, chanting anti- government slogans and calling police butchers, rallied in marches that turned violent when demonstrators began throwing stones and firebombs at nearby riot police.

Rioting quickly spread Sunday from Athens to Thessaloniki, the western port city of Patras, the central cities of Ioannina and Volos and the southern Mediterranean island of Crete, as soon as news of the shooting got out.

More than 25 police officers were reported injured in the rioting, including four hospitalized with serious injuries.

Eleven civilians were reported injured in Athens, three in Patras and one in Thessaloniki. They were taken to hospitals with injuries sustained during the riots. Dozens more were arrested, police said.

Greece's conservative government appealed for calm after a night of some of the worst riots in years. Despite the pleas, violence erupted again Sunday.

"The government will apply the law to stop the violence. Everyone has the right to protest, but violence and the destruction of public and private property will not be tolerated," Interior Minister Prokopis Pavlopoulos said as he emerged from talks with the prime minister.

Pavlopoulos offered his resignation to Karamanlis, who refused the overture.

The shooting has been described by the media as one of the worst incidents of police violence in more than a decade and the first time since 1985 that Greek police have killed a minor.

Karamanlis' government faced a series of protests from labour groups and students in recent months.

Reports said that Karamanlis, whose government rules with a slim majority, may be forced to call early elections.

Just as questioning began of the two arrested police officers who were suspects in the shooting, dozens of people staged a march outside police headquarters where the men were taken.

"The government believes that it can rule with an iron fist, but no more. People have had enough," said 45-year-old architect Nikos Polynikas.

Public unrest has grown with the conservative government's austerity measures, and labour unions have called for a 24-hour strike on Wednesday over privatizations, pension reforms and the cost of living. One-fifth of Greeks live below the poverty line. dpa