Anti-austerity Syriza party has won Greece’s general election, putting the country on a possible collision course with the EU over its massive bailout.
With nearly 75% of the votes counted, Syriza is projected to win 149 seats, just two short of an absolute majority, though that number could change.
Left-wing party leader Alexis Tsipras, who wants to renegotiate Greece’s debt, said “the Greeks wrote history”.
The governing centre-right New Democracy has come a distant second.
Outgoing Prime Minister Antonis Samaras has admitted defeat and phoned Mr Tsipras to congratulate him.
Syriza’s result will send shockwaves through Europe, the BBC’s Gavin Hewitt in Athens reports.
A majority of voters in Greece have essentially rejected a core policy for dealing with the eurozone crisis as devised by Brussels and Berlin, our correspondent adds.
In Germany, Bundesbank President Jens Weidmann said he hoped “the new Greek government will not make promises it cannot keep and the country cannot afford”.
The election result is expected to be one of the main issues during Monday’s meeting of 19 eurozone finance ministers.
Belgium’s representative Johan Van Overtveld was quoted by VRT network as saying that Greece “must respect the rules of monetary union”, although he added that there was room for some – but not much – flexibility.
British Prime Minister David Cameron – whose country is not a member of the eurozone – said the result of the Greek election would “increase economic uncertainty across Europe”.
Meanwhile, the euro fell to $1.1098 against the dollar – the lowest level in more than 11 years.