Athenians reached out to receive free produce handed out by farmers in protest against the government's proposal to overhaul the country's ailing pension system.

Farmers who have been blocking motorways across the country on and off for days in protest at planned to cut tax breaks for farming as well as pensions remained defiant.

In a symbolic protest, they gave out about 50 tonnes of produce in under an hour in a poor, working-class Athens neighbourhood, where a few hundred Greeks jostled with one another for free bags of potatoes, lettuce and fruit.

Ferries were docked at Greek ports as sailors kicked off their second 48-hour strike this week, adding to a groundswell of public discontent over plans to reform the country's struggling pension system.

Prime Minister Alexis Tsipras has launched a vocal defence of the plan, saying that the country had no choice but to reform a pension system which had created chronic deficits and would collapse if left unchanged.

Greeks, many of whom will see contributions jump to about 20 percent of monthly earnings to prop up the new pension system, have responded angrily to the proposed changes, staging a series of rallies and protests across the country in recent weeks.

Under the plan, which Greece must adopt for its international lenders to complete their first review of its latest bailout, the country's pension funds would be merged into one together with cutbacks worth 1 percent of gross domestic product a year.

"We're striking because our main pension fund, the oldest in Greece, will close," said Lefteris Saridakis, head of a union representing staff on passenger ships.

He said the workers planned to step up action when the bill is tabled in parliament next month.