Three people were killed Wednesday in a fire that broke out at a bank during violent protests against harsh new spending cuts, police said.

Hooded protesters firebombed a Marfin Bank branch near the parliament building, trapping at least 20 employees and customers inside, witnesses told Xinhua.

Police said the victims -- two women and one man -- were all employees of the bank.

The violence broke out as protesters of all ages gathered in central Athens to denounce government policies implemented in exchange for a 110-billion-euro (146-billion-U.S.-dollar) rescue package by the European Union and the International Monetary Fund.

Demonstrators chanting "thieves, thieves" marched toward the parliament and attempted to break through a cordon of riot police guarding the building.

"Why should I pay for others' mistakes and scandals? Why should my children pay when it was not their fault? Greece almost reached bankruptcy. How can I guarantee them that in a few months or years they will not ask for more sacrifices from us, while people responsible do not pay?" Kostas Fournaris, a 53-year-old civil servant, told Xinhua.

The first battles between police and demonstrators erupted near the Polytechnion, or the Technical University of Athens.

Protesters threw paving stones at the police, who responded with tear gas and stun grenades. One protester threw a Molotov cocktail at a bank that quickly went up in flames.

Demonstrators also set dustbins on fire and attacked authorities with firebombs in the central district of Exarchia, where the death of a teenager by police fire in December 2008 sparked some of the worst riots Greece has seen in the past 30 years.

Similar violence also broke out in the northern city of Thessaloniki, where about 20,000 people marched through the city center, with youths smashing the windows of stores and fast food restaurants.

The demonstrations came amid a 24-hour national strike that grounded all flights to and from Greece, shut down ports, schools and government services and left hospitals working with emergency staff.

Archeological sites across the country, such as the Acropolis, also remained closed, and Greek television and radio channels broadcast music, as journalists took part in the strike.

The protests in Athens were some of the largest in recent years, with some estimates putting the crowd at 60,000 people. Authorities put the number at above 25,000.

Prime Minister George Papandreou Sunday announced severe austerity measures, including salary and pension cuts for civil workers, and another round of consumer tax increases to pull cash-strapped Greece away from bankruptcy.