"If yesterday's events are anything to go by, we will probably be seeing scattered skirmishes throughout the day between anarchist groups and police," Al Jazeera's Nicole Itano, reporting in Athens, said.
"At the moment, the mood is certainly very tense and there is widespread anger across the city about the young boy's death. This anger is both among the hardcore anti-establishment groups who are causing most of the damage, but also really among a wider swathe of the community."
Protesters had smashed the windows of banks, businesses and government ministries, and set fire to rubbish bins, filling the air with acrid smoke as police and rioters clashed late into Monday night.
A major department store and a huge Christmas tree outside parliament were also set alight. More than 200 fires were started in Athens on Monday, the fire department said.
The police said that some of the protesters were attacking officers with swords and slingshots stolen from an Athens weapons shop.
Costas Karamanlis, the prime minister, called an emergency cabinet meeting as police fired tear gas in a bid to clear the centre of the Greek capital.
Karamanlis vowed to end the country's worst unrest in decades, but a government spokesman denied reports that the government planned to declare martial law.
|The funeral of Grigoropoulos will be held on Tuesday
As the violence raged, about 10,000 protesters from the Communist Party of Greece and the Coalition of the Left marched through Athens to protest against the killing of 15-year-old Alexandros Grigoropoulos in the traditionally left-wing Exarchia district on Saturday.
Alexis Tsipras, the coalition leader, said the teenager's shooting had resulted in "a spontaneous youthful uprising".
"The prime minister has a deep political responsibility. But instead of taking it, he is rejecting the ... resignations of the responsible ministers, he is adopting the version of an isolated incident and barricading himself behind broken storefronts," he said.
Another demonstration was scheduled for Tuesday, and a general strike called by unions before the incident will be held on Wednesday.
Two officers have been charged over the shooting - one with premeditated manslaughter and the illegal use of a weapon and the other as an accomplice.
They are due to appear before a court on Wednesday and both have been suspended - along with the Exarchia precinct police chief.
Panayiotis Stathis, a police spokesman, said 89 people had been arrested for attacks on police, vandalism and looting since the violence began.
Another 79 people had been detained for questioning over the riots in which dozens of police officers have been injured.
Small groups of youths continued to occupy university campuses in the centre of the capital, throwing stones and Molotov cocktails at police.
In Germany, more than 15 people occupied the Greek consulate in the heart of Berlin's downtown shopping district on Monday, hanging a banner and throwing down pamphlets to urge resistance against state force.
No violence was reported and the protesters walked out of the building peacefully, past police officers, eight hours later.
Demonstrations also took place in London and Nicosia in Cyprus.
On Monday, hundreds of students clashed with police in the northern Greek city of Thessaloniki.
Around 300 people threw fire bombs at riot police and attacked cars and shops as demonstrations spilled over into violence.
|Youths took over the Greek consulate in Berlin to protest the shooting [Reuters]
Two people were detained as police used tear gas against the rioters.
There were also clashes in the central city of Trikala, where dozens of youths broke off from a student demonstration and attacked banks, shops and cars on the city's main square.
The popularity of Karamanlis has been hit by the poor state of the country's economy and a number of scandals that saw three ministers leave government last year.
After the cabinet meeting on Monday, his government defended the handling of the unrest.
Prokopis Pavlopoulos, the Greek interior minister who offered to resign on Sunday, said the police action had been intended to "protect human life and property".
"The state machinery has protected more things than those that were threatened ... it is there to protect human life and everything else, without threatening democracy," the minister said.