A man sits on a couch dragged from a looted cafe and used to construct a roadblock, as the charred remains of a store selling sports good are seen in the background, near the National Technical University in central Athens. (Thanassis Stavrakis/Associated Press)

Police stations in Athens were attacked by high school students wielding stones and firebombs Thursday as the city entered its sixth day of riots sparked by the death of a teenager shot by police on the weekend.

The unrest also spread to several other European cities as youths damaged police vehicles and threw bottles at officers.

An estimated Greek police 20 stations came under siege Thursday morning, as protesters also tossed over cars and barricaded streets. At least one man was injured — one of at least 70 people wounded since demonstrations began on Saturday.

"An elderly bystander was taken to hospital after he was hit by a rock," an unnamed police official told Reuters.

Central Athens was reportedly calmer than in previous days thanks to the end of Wednesday's 24-hour general strike. But clashes between police and students lasted through the night, culminating with the attacks on the police stations.

At least 500 people descended on the central police station in the northern city of Thessaloniki, according to Reuters. Groups of people were reportedly gathering in the western port of Patras and Ioannina.

A student rally is scheduled for Thursday afternoon, with more protests planned on Friday and Monday.

"The government has shown it cannot handle this. If police start imposing the law everyone will say the military junta is back," electrician Yannis Kalaitzakis told Reuters.

"The government is stuck between a rock and a hard place."

Greek authorities have charged police officer Epaminondas Korkoneas, 37, with murder in the shooting of Alexandros Grigoropoulos, 15, in the volatile central Athens district of Exarchia on Saturday night. A second officer, his partner, has been charged as an accomplice.

Police apologize

The shooting has inflamed what had already been rampant discontent over the conservative government's economic policies. More than 100 people have been arrested, including four on Thursday, during some of the worst protests Greece has seen in decades.

The police association has apologized to the teenager's family but the death has spurred six days of rioting throughout Greece.

On Wednesday, Athens's main courthouse came under attack when hundreds of protesters threw rocks and firebombs as the two accused police officers testified at a pre-trial hearing inside. Korkoneas and his partner were sent to jail pending trial by a prosecutor.

Observers have said the growing hostility among Greek youth is being fed by public discontent over low wages, frequent public corruption scandals and a strong historic distrust of government that is rooted in past political upheavals.

Greece's opposition socialist party, which is currently leading in the polls, has called for an election, lambasting the government for failing to settle the riots.

An opinion poll published Wednesday showed 68 per cent of Greeks disapproved of the government's handling of the crisis.

"We demand accountability, that this government resigns, and that this farce comes to an end," said 28-year-old Spyros Potamias, an architecture student who joined an occupation at Athens Polytechnic. "This is about our future."

Prime Minister Costas Karamanlis, who has said the government will provide financial support to businesses that have been damaged during the rioting, was in Brussels for an EU summit on Thursday.

He has appealed to the public for calm — a call echoed by the country's influential Orthodox Church.

"This tragedy cannot be resolved by burning and destroying the property of people who themselves have problems," said Church leader Archbishop Ieronymos.

European violence

Violence spread to other parts of Europe Thursday and late Wednesday.

In Denmark, protesters threw bottles and paint at police in downtown Copenhagen. Dozens of people were detained and later released.

Angry youths in Spain attacked banks, shops and a police station in separate demonstrations in Madrid and Barcelona late Wednesday that each drew about 200 people.

Protesters in France set fire to two cars and a garbage can outside the Greek consulate in Bordeaux early Thursday.

"For the moment, we can't go farther with our conclusions and say that there's a danger of contagion of the Greek situation into France. All of that is being watched," French Interior Ministry spokesman Gerard Gachet told The Associated Press.

At least some of the protests appear to have been organized over the internet, showing how quickly a message can be spread, particularly among tech-savvy youth. One website that Greek protesters have been using to update each other claims there have been sympathy protests in nearly 20 countries.

With files from the Associated Press