Chris Morris, BBC Europe correspondent Athens

This is a turning point for the eurozone crisis. If you talk to Syriza's economic leaders, they say they have everything costed. But what the party wants is a European debt conference, to look Europe's leaders in the eyes and say, now we have to talk seriously about this.

Mark Lowen, BBC correspondent in Athens

This is a result that will have profound implications and send shock waves far beyond Greece's borders.

Syriza supporters celebrating in Greece's second city, Thessaloniki, a New Democracy stronghold.

Image source, AP

Outgoing Prime Minister Antonis Samaras is expected to make a statement shortly in Athens, with partial results suggesting his conservative New Democracy party has suffered a crushing defeat to Syriza.

Sam Marner in Sheffield emails: The Greeks are a tough people, but they don't suffer fools. Tolerating austerity while the elite are exempt from the same suffering is clearly something they are not prepared to accept, and they are all the better for that.

Imelda Flattery, BBC News Athens

tweets:, external Definition of knife edge. Syriza needs 151 seats for an absolute majority. Latest projections say 150. (Error margin 149-151)

Nick Malkoutzis, deputy editor of Greek daily Kathimerini English edition

tweets, external: We now seem to be heading for what opinion polls predicted: Syriza short of majority/with weak one & no obvious allies

Announcing the official projection, Greek electoral official Michael Cariotoglou stressed there was still a margin of error that could lead to a swing of a few seats either way for Syriza. He did not say when the final result would be known.

Syriza's closest rival, New Democracy, is almost nine percentage points behind Syriza but anything less than 151 seats will deny the radical left party an outright victory in parliament. Even with 151 seats, Syriza would be looking for a coalition partner, Greek analysts say.

Another New Democracy figure, Administrative Reform Minister Kyriakos Mitsotakis, has conceded victory, congratulating Syriza and saying its victory "cannot be questioned", AP reports.

"It is evident the Greek people believed there is another way forward than the one described by the government," he said. "For the good of the country, I hope they are right."

First official projection gives anti-austerity party Syriza victory in Greece, with 36.5% of the vote and 149-151 seats in the 300-member parliament.

"It's a really good night, Frau Merkel": banner written in German outside Syriza headquarters in Athens. Photo tweeted, external by journalist Andres Mourenza.

Image source, Andres Mourenza

Spyros Gkelis, Athens

tweets, external: I see Left parties of #Portugal #Spain #UK #Ireland and more celebrating #Syriza's victory; unprecedented, at least in #Greece

Far-left Die Linke chair Katja Kipping in Germany

tweets (in German, external): A beautiful day. A European spring is starting in Greece

Panagiotis Tsantis in Ann Arbor, US emails: In order for Greece to turn the page, many changes to its foreign and domestic policies must occur. There needs to be a strong enforcement of domestic tax policies. No more tax loopholes. Furthermore, the new parliament should focus on how to get businesses to invest in the country as a whole. Greece must focus on marketing their factors of production, so to increase Foreign Direct Investment. Only then will Greece be able to start to recover.

George Papandreou (shown below, after voting in Athens), the former prime minister now leading a new centre-left party called the Movement of Democratic Socialists, has said, "No party, even with a majority, can handle the current situation alone," according to Greek newspaper Kathimerini.

Exit polls suggest his party will fail to clear the threshold for entering parliament. As leader of the socialist party Pasok, Mr Papandreou took power in 2009, when he tried to tackle the economic crisis with austerity measures. He stepped down in 2012 to make way for a short-lived technocratic government under economist Lucas Papademos.

Image source, EPA

Athens-based journalist Nick Barnets

tweets, external: Alexis Tsipras has arrived at Syriza's campaign HQ.

Initial results have begun coming in. Greece's election commission says after 17.66% of the votes counted, anti-austerity Syriza has polled 35.03%; conservative New Democracy 29.31%; far-right Golden Dawn 6.29%; centrist The River 5.59%, the communist KKE 5.30%; and socialist Pasok 5.21%.

Syriza's manifesto has four "pillars" which include confronting the humanitarian crisis and restarting the Greek economy. But perhaps most significantly it calls for a write-off of the "greater part" of the country's public debt.