|Greece's ageing population means its pension system runs the risk of collapsing [EPA]|
Much of Greece was brought to a standstill as tens of thousands of striking public sector workers marched through Athens to protest against proposed government changes to the pension system.
Flights were grounded and urban transport came to a halt after the 24-hour strike began at midnight on Wednesday.
An estimated 40,000 people joined the rally, the biggest in the country for three years.
Ferries were stopped across the Aegean islands, public services were closed and hospitals worked with emergency staff.
Protesters shouted slogans against the newly elected conservative government as thousands of police in riot gear stood guard.
Demonstrations were held in other cities as unions hailed what they described as an "unprecedented turnout".
Police in the capital made three arrests and used teargas after clashes between activists and officers.
Just nine trains were scheduled to run nationwide, whilst all civil air traffic was halted as air controllers joined the strike.
The country's justice system was already at a standstill as lawyers and court officials continued a two-day stoppage that began on Tuesday.
In addition to transport, other affected areas included the health, education, banking and media sectors.
In the health sector only emergencies were being handled as doctors, pharmacists and dentists joined the movement.
Schools, public offices, banks as well as post offices, the energy utility and OTE, the national telecommunications operator, also shut down.
Athens' metro and bus services ran for five hours in the middle of the day - but only to guarantee that as many demonstrators as possible attended the protest in the city centre.
Efstathios Anestis of the private sector umbrella union GSEE said that "participation is almost total. There is overwhelming outrage and condemnation at the government's policies".
GSEE and its public sector equivalent Adedy, which jointly represent more than 2.5 million workers, have rejected repeated calls from the government to attend talks on pension reforms and have staged several rallies instead.
The protesters marched to parliament carrying a coffin with a sign reading "Social Security". They chanted anti-government slogans and waved banners saying: "The dialogue is a fraud."
Like other EU countries with ageing populations, Greece is struggling to restructure its pension system before it collapses.
Experts say Greece's fragmented social security system, which runs deficits twice the country's 200 billion euro annual economic output, is expected to collapse in 15 years if no measures are taken.
Government officials declined to comment on the strike.
The government of Costas Karamanlis won a second term in office in September promising no pension rights would be affected.
But shortly after winning, it proposed measures to encourage workers to stay in work beyond the age of 65 and a review of pensions for women and disabled workers.
|All civil air traffic ceased because of the strike [AFP]|