(CNN) -- The first clashes were reported Saturday as thousands of Greek protesters and police fanned out ahead of an expected announcement by the country's prime minister that additional austerity measures are on the way.
Some 5,000 police officers were deployed and about a growing number of protesters -- at least 15,000 -- were already gathered at the various meeting points, police told CNN. The number of protesters is expected to swell to coincide with Prime Minister George Papandreou's speech.
According to police, a large number of the protesters are taxi drivers who are opposing reforms to open up their sector to competition.
Police on Saturday reported the first, minor, clashes between police and protesters in the northern city of Thessaloniki.
"Protesters have been hurling stones and other objects at police officers around the venue" where the prime minister is to speak, police spokesman Athanassios Kokkalakis told CNN. "Police responded with controlled use of tear gas, but overall things remain calm."
According to local reports, Papandreou is expected to announce more austerity measures ahead of a new round of talks with Greece's lenders next. It would be the latest in a round of increasing austerity measures that have been met by protests.
Papandreou is likely to announce measures such as 10,000 immediate job cuts in the public sector. He is also expected to say that tens of thousands more civil workers are to lose their jobs within the next year.
If these measures are announced, they will be the first mass cuts in the public sector since Greece undertook a bailout plan this Spring.
At the end of June, the Greek parliament voted to implement a round of austerity measures in hopes of avoiding defaulting on the government's debt.
That decision came amid a round of large-scale protests in the streets, with riot police firing tear gas.
Demonstrators rejected measures including reductions in the pay of public workers and social security funding and an increase in the attrition of public jobs. Last year, an austerity package included pension cuts, higher taxes, and a hike in retirement age to 65 from as low as 61.
Of Saturday's demonstrations, the biggest are expected to be organized by the Confederation of Greek Labor, which represents some two million workers, and the the civil servants' union ADEDY, which represents 800,000 public workers who are facing imminent salary cuts.
A default by Greece would send shock waves through the European banking sector and potentially dent global economic confidence.
Markets dropped sharply Friday as rumors of a possible Greek default circled the globe. The default could come as early as this weekend. Whether or not something happens in Greece will largely rule market sentiment as the market opens in New York Monday.
Investors sold stocks Friday in fear that Athens may not get its next installment of bailout money from the European Union, International Monetary Fund and European Central Bank and that the bankruptcy could come to light over the weekend.
