All sectors, from dentists, state hospital doctors and lawyers to shop owners, tax office workers, pharmacists, teachers and dock workers walked off the job ahead of a Parliamentary vote Thursday on new austerity measures which include new taxes and the suspension of tens of thousands of civil servants.
Flights were grounded in the morning but some resumed at noon after air traffic controllers scaled back their initial strike plan from 48 hours to 12. Dozens of domestic and international flights were still canceled throughout the day.
Ferries remained tied up in port, while public transport workers staged work stoppages but were to keep buses, trolleys and the Athens metro running for most of the day.
In Parliament, Finance Minister Evangelos Venizelos told lawmakers that Greeks had no choice but to accept the hardship.
"We have to explain to all these indignant people who see their lives changing that what the country is experiencing is not the worst stage of the crisis," he said. "It is an anguished and necessary effort to avoid the ultimate, deepest and harshest level of the crisis. The difference between a difficult situation and a catastrophe is immense."
About 3,000 police deployed in central Athens, shutting down two metro stations near Parliament as protest marches began. Police estimated the crowd at least 70,000.
Protesters converged on the square in front of Parliament, banging drums, chanting slogans against the government and Greece's international creditors who have pressured the country to push through rounds of tax hikes and spending cuts.
At least 15,000 demonstrators also gathered in Thessaloniki, Greece's second-largest city.
"We just can't take it any more. There is desperation, anger and bitterness," said Nikos Anastasopoulos, head of a workers' union for an Athens municipality.
Other municipal workers said they had no option but to take to the streets.