Three people died in a fire in a bank started by Greek protesters in central Athens on Wednesday, police said during demonstrations against government austerity measures.
The bodies of two men and a woman were discovered inside the bank branch of Marfin. Several people were still believed to be trapped inside.
"The fire brigade has found the bodies of three people in Marfin Bank which was set on fire earlier by protesters," Attica police spokesman Panagiotis Papapetropoulos said.
He said that protesters had also set fire to several other buildings, including the Athens Municipality office, located in the heart of the Greek capital. Police and firefighters were in the process of evacuating people from the area, said Papapetropoulos.
The clashes in Athens came as tens of thousands of people joined marches in cities across the country to protest a government bailout for austerity deal.
Hundreds of demonstrators hurled rocks and chunks of marble at police, set cars, kiosks and garbage cans on fire and tried repeatedly to storm parliament.
Riot police retaliated by firing several round of tear gas.
Masked youths threw homemade petrol bombs at dozens of shop windows, causing one of Athens' busy streets to fill up with giant clouds of dark grey smoke.
The rioting took place shortly after tens of thousands of people were marching in central Athens, in the biggest protest over the Mediterranean country's debt crisis.
Greek union leaders and media reports estimated that between 200,000 and 250,000 people took part in the marches. Police put the number at roughly 100,000.
The latest protests come just days after the cash-strapped government unveiled plans for further drastic budget cuts in exchange for a 110-billion-euro ($145-billion) rescue by the European Union and the International Monetary Fund (IMF).
Wednesday's protests also coincide with the start of a 24-hour general strike.
Ministries, tax offices, schools, public services and hospitals remained closed after public sector workers launched a 48-hour national strike on Tuesday.
Private sector workers joined in Wednesday, shutting down transport in major cities and grounding flights at airports in the third joint walkout since the start of the year.
"The measures are going to be the end for us - how will I be able to survive?" said Artimis Batza-Pnadou, a cleaner for the Salamina Municipality whose salary has been reduced by 250 euros, told DPA.
"Now I earn 950 euros a month and after I pay my rent, which is 400 euros, how am I supposed to raise my children on what's left?" the divorced mother of three said.
The usually bustling port of Pireaus was eerily empty, while a 24-hour news blackout was in place after journalists refused to show up for work.
EU leaders agreed Sunday to activate the three-year Greek rescue programme.
Athens plans to save around 30 billion euros by 2012 by cutting pensions and public servants pay and hiking consumer taxes.
The Socialist government of Prime Minister George Papandreaou on Tuesday submitted its austerity bill to Parliament.
Public anger is expected to grow with more than one in two Greeks saying they are prepared to take to the streets to fight the austerity plans.
Running a debt of more than 300 billion euros and a budget deficit of 13.6 of gross domestic product, Greece is in urgent need of funds before May 19 in order to refinance a 9-billion-euro, 10-year bond.