|The country's biggest general strike brought air, land and sea transportation to a halt [EPA]|
Tens of thousands of workers have jammed the streets in Greece to protest the government's plan to reform the country's social system, bringing two major cities to a standstill.
At least five people including four police were reportedly injured during the 24-hour strike which began at midnight on Tuesday.
Police fired tear gas in brief clashes with about 80,000 demonstrators in central Athens and some 30,000 in the northern city of Thessaloniki.
At least 10 protesters were detained.
Labour unions oppose government efforts to reform Greece's fractured pension system including attempts to unify the country's roughly 170 pension funds, many fearing the move could cut pensions and raise retirement ages.
A similar attempt in 2001 sparked massive demonstrations and almost brought down the then socialist government.
"The rallies in Athens and in other cities had unprecedented participation," said Yiannis Panagopoulos, head of GSEE, one of the two major unions that called the strike. "It was at least double that of 2001."
Air, land and sea transport services ground to a halt, hospitals only took in emergency cases, while journalists walked off the job, cancelling television and radio news programmes.
The courts were also shut down for a second day as lawyers and judges began a 48-hour strike on Tuesday.
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.
More strikes are expected next week when more workers from other professions join the strike.