Opinion polls published on the last day of campaigning before general elections in Greece show the left-wing Syriza party has increased its lead over the governing conservatives, but would still need to form a coalition government.

Five surveys published late Thursday and Friday give Alexis Tsipras' Syriza an advantage of between 5.2 and 6.7 percentage points over conservative Prime Minister Antonis Samaras' New Democracy — a gain of about 2 points in a week.

Greeks head to the polls Sunday. The polls also show gains for the extreme right Golden Dawn which is vying for third place.

Syriza has promised to challenge bailout agreements to press for better repayment terms and massive debt forgiveness — a promise the conservatives call unrealistic and potentially fatal for the country's fragile recovery.