First round for election for president tonight

But the backing of the coalition government, which controls 155 deputies, garners will be closely watched as a sign of momentum for or against it ahead of a final, decisive vote on Dec. 29 when the super majority required for victory falls to 180.

Support of below 160 votes would be considered a blow for the government, while 170 or above would be considered a strong show that suggests Samaras can scrape together the votes needed in the final round, coalition officials have said.

Fears of a new chapter of prolonged political uncertainty have sent Greek stocks and bonds crashing since Samaras last week announced the presidential vote would be held this month instead of February. Greek stocks fell over 20% in three days last week while 10-year bond yields leapt over 9%.

"Greeks demand that we fight united, to safeguard everything we achieved with bloody sacrifices in the last few years, and lead them safely to finally exit the crisis," Samaras said in an appeal to lawmakers on Tuesday.

Samaras has warned of a "catastrophic" return to the height of Greece's debt crisis - when it risked being driven out of the euro zone - if his government falls, while SYRIZA has accused him of scare-mongering and blackmail to win support. Samaras is an "architect of chaos, who invests in a climate of fear-mongering", SYRIZA spokesman Panos Skourletis said.

Both sides are battling to win over a pool of about 24 independent lawmakers whose votes will decide the outcome. Of these, seven have said they will support Samaras and eight have declared against.

Samaras will also need the support of at least a few lawmakers from two small parties, the Independent Greeks and the Democratic Left, to win the final round but both parties have so far said they would vote against the government.

The second round vote is scheduled for Dec. 23 with the third, crucial one, coming on Dec. 29.