Alexis Tsipras has said his leftist Syriza party’s win at a Greek general election is a “great victory of the people”.
Mr Tsipras, who appeared at a rally of supporters in Athens, said he felt “vindicated” in calling the poll after quitting in August.
With half of the vote counted, Syriza won 35.54% of the vote, according to Interior Ministry data.
The conservative New Democracy is on 28.07% – which prompted its leader Vangelis Meimarakis to concede defeat.
Based on the vote count, Syriza would get 145 seats in the 300-seat parliament and New Democracy 75.
The Nazi-inspired Golden Dawn was coming in third with 7.1%.
Syriza is likely to fall short of an outright majority and would need to form a coalition.
However, a source within the party told the Reuters news agency that Mr Tsipras will form a government “within three days”, and the Independent Greeks party head said it will join the party in a coalition government.
During the campaign, Mr Meimarakis had said his party would join Syriza in a national unity government but Mr Tsipras has repeatedly ruled this out.
As the votes were counted, Mr Meimarakis said: “The election result appears to be forming comprehensively with Syriza and Mr Tsipras coming first.
“I congratulate him and call on him to form the government that is necessary, and bring the (proposal) to parliament.”
Declaring his victory, Mr Tsipras said: “In Europe today, Greece and the Greek people are synonymous with resistance and dignity, and this struggle will be continued together for another four years.
“We have difficulties ahead, but we are also on firm ground. We wont recover from the struggle by magic, but it can happen with hard work.”
A Syriza party spokeswoman said the party would implement the bailout deal it previously agreed with European Union lenders.
Olga Gerovassili said: “This will be a four-year term government with a strong parliamentary majority, which will implement the programme it promised.
“It will continue the tough negotiations with the lenders, realising that this is the beginning of a battle.”
The early vote, the fifth general election in the country in six years, was triggered by Mr Tsipras’s resignation as prime minister last month.
The move was designed to refresh his mandate amid a rebellion within his party over his acceptance of a painful third international bailout.
Mr Meimarakis has accused him of breaking promises by abandoning his anti-bailout stance and negotiating an €86bn (£62.6bn) package with EU creditors.
Mr Tsipras’s party regards New Democracy as part of the old establishment responsible for the country’s economic woes which “piled debts on Greeks”.
In opinion polls in the run-up to the vote, the two rivals had rarely been half a percentage point apart.
Based on the early results, the turnout was 55.4% while the January election was won by Mr Tsipras with 63.6% of the vote.
The head of the Eurogroup Jeroen Dijsselbloem congratulated Mr Tsipras on his win and said he looked forward to the swift formation of a new government with a strong mandate to continue implementing the bailout deal.
French President Francois Hollande said the victory was an “important success” for both Greece and Europe.
He said: “This is an important outcome for Greece which will now live through a stabilisation period with a solid majority.” – Sky News.
