The insurgent leftist Syriza party was heading to a momentous election victory in Greece on Sunday night, throwing down a challenge to European governments determined to resist its demands for extensive debt relief and an end to austerity.

With 54.5 per cent of votes counted, Syriza led New Democracy, the ruling centre-right party, by 35.9 per cent to 28.3 per cent, giving Syriza a projected 149 seats — three short of an absolute majority. The far-right Golden Dawn party was third with 6.4 per cent, and the centre-left To Potami (“The River”) fourth with 5.9 per cent.

A Syriza government free of the need for coalition allies would strengthen the leverage of the party’s militant far-left wing — and see the eurozone’s most explicitly anti-austerity government in power since the financial crisis erupted in 2008. Led by Alexis Tsipras, the party’s 40-year-old leader, it would also give Greece one of the most leftwing governments seen in a European democracy since the second world war.