Greek workers will begin a 48-hour strike tomorrow to protest against a new round of austerity cuts that unions say will devastate the poor and drive a failing economy to collapse.

The walkout is being called by Greece's two biggest labour organisations.

It will be the third major strike in two months against a package of spending cuts and reforms that Prime Minister Antonis Samaras's government is trying to push through parliament to unlock aid.

Athens needs parliamentary approval for the package - which includes slashing pensions by as much as a quarter for some and scrapping holiday bonuses - to ensure its European Union and International Monetary Fund lenders release more than €31bn of aid, much of it aimed at shoring up banks.

The government has implored Greeks to endure the cuts in a bid to avoid national bankruptcy and insists they will be the last round of pain.

The strike is timed to coincide with a crucial vote on Wednesday, when the government is expected to just about win backing for austerity cuts and labour reforms that the smallest party in Mr Samaras's coalition has refused to back.

Transport is expected to be severely disrupted across the country as trains, buses and the subway come to a halt. Many flights have been cancelled, ships will remain tied up at ports and taxi drivers plan to stay off the streets.

Schools, banks and local government offices will be shut, while hospitals are expected to work on emergency staffing.

olice were beefing up security for midday rallies in Athens that often culminate in a small-scale rioting and clashes with hooded protesters, but officials said violence was more likely during the parliamentary vote on Wednesday.

Greece has gone through several rounds of austerity that has helped shrink its economy by a fifth since the debt crisis exploded but failed to bring its finances back in order.

Anger has given away to a sense of resignation for many Greeks, who warn the latest cuts could tear a beleaguered society apart.