"Citizens sent a very clear message that they don't want this (austerity) policy to continue," PASOK spokeswoman Fofi Gennimata said. "It was a very great defeat for us."
PASOK, which has spent 21 years in government since 1981 and stormed to victory with more than 43 percent in 2009, saw its support slashed to 13.18 percent. It will have just 41 seats, compared to 160 in the last election.
Sunday's turnout was 65 percent — a low figure for the country, where voting is officially compulsory, although no sanctions are applied for not casting a ballot. A total of seven parties won representation.
Another four small parties fell just short of the three percent parliamentary entry threshold, getting just over ten percent between them.
Samaras is to meet Papoulias to strike a coalition agreement. He will then meet with the leaders of PASOK and Syriza, as well as the head of a smaller, more moderate left-wing party.
If he fails to form a government, the mandate will go to the second party for another three days, and then to the third party. If no deal can be reached by May 17, the country will hold new elections a month later.
"A nightmare of no government, with new elections looming in the background," Ta Nea daily said in its main headline.
Agapitos said Greeks on Sunday were carried away by their feelings.
"In the next elections, people will either come to their senses and look at their options ... and if that happens the most realistic proposal will win, but if the current tend continues, the lack of government will continue and things will become even more difficult," he said.
"I can see no good reason why anyone should want to invest in Greece when it doesn't have a government and it is unclear what strategy it will pursue."
The president of the European Parliament, Martin Schulz, said the election results needed to be analyzed calmly.
"The aim of negotiations in Greece should be to form a coalition that would stick to Greece's commitment to the European Union," Schulz said in Berlin. He noted the results emphasized the need for the EU to adopt a comprehensive package to stimulate economic growth.
Both Samaras and PASOK leader Evangelos Venizelos indicated any unity government would have to include more than just their two parties.
But in a note that will likely raise alarm among Greece's creditors, Samaras insisted any coalition should renegotiate the terms of the country's bailout.
"We are ready to take up the responsibility to form a new government of national salvation with two exclusive aims: For Greece to remain in the euro and to amend the terms of the loan agreements so that there is economic growth and relief for Greek society," he said.
Riding high on his gains, Syriza leader Alexis Tsipras, aged 38, stuck to his anti-bailout position.
"The people have rewarded a proposal made by us to form a government of the left that will cancel the loan agreements and overturn the course of our people toward misery," he said.
Raf Casert in Brussels contributed
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