Greek workers have begun their first mass confrontation with Greece's three-month-old coalition government, grounding flights, disrupting local transport and shutting public service offices.

The general strike is being backed by the country's biggest private sector force, the General Confederation of Greek workers (GSEE), the union of civil servants (ADEDY), and militant unionists attached to the KKE communist party.

All three groups are holding hold mass demonstrations in Athens – and some 65 cities and major towns nationwide – before protesters march on the Greek parliament.

"We call on everyone to take part in the strike and resist the austerity measures that hurt Greek people and the economy," said unionist Despina Spanou of ADEDY. "This strike is only the beginning in our fight."

The traditional summer break has allowed the conservative-led government of prime minister Antonis Samaras to enjoy relative calm on the streets since taking power in June.

About 3,000 police officers – twice the number usually deployed – are standing guard in the centre of Athens as authorities brace for the rioting that has marked past rallies. Athens last witnessed serious violence in February, when protesters set shops and banks ablaze as parliament approved an austerity bill.

Ships will stay docked, shops have pulled down shutters, and museums and monuments will be closed to visitors throughout the day. Air traffic controllers are to walk off the job for three hours and hospitals will operate on emergency staff.

Even tax collectors have said they will join in the action which has also closed archaeological sites, including the ancient Acropolis.

Much of the union anger is directed at spending cuts worth nearly €12bn (£9.5bn) over the next two years that Greece has promised the European Union and International Monetary Fund to secure its next tranche of aid.

The bulk of those cuts are expected from slashing wages, pensions and welfare benefits, heaping a new wave of misery on Greeks, who say repeated rounds of austerity have pushed them to the brink yet failed to transform the country for the better.

At a time when unemployment is at a record high – hitting almost 24% at a national level and 55% among young Greeks, the highest in Europe – protesters say the new round of belt-tightening, encapsulated in the €11.9bn package of cuts the government has been called to pass in exchange for extra aid, is nothing short of "unfair and anti-social".

A survey by the MRB polling agency last week showed that more than 90% of Greeks believe the planned cuts are unfair and burden the poor, with the vast majority expecting more austerity in coming years.

But with Greece facing certain bankruptcy and a potential eurozone exit without further aid, Samaras's government has little choice but to push through the unpopular measures, which have also exposed fissures in his fragile coalition.

With the country in its fifth year of recession and no light at the end of the austerity tunnel, analysts warn that Greek patience is wearing thin and a strong public backlash could tear apart the weak coalition.

"What people want to tell Samaras is that they are hurt and Samaras could use this to demand concessions from the troika," said MRB polling director Dimitris Mavros.

"The people are willing to give the government time, but on certain conditions like cracking down on tax evasion and securing a bailout extension. If the government succeeds in that, its life will also be extended."