Greece's lawmakers are to cast ballots in the first round of a crucial presidential election that could see the government collapse if its nominee does not garner enough votes.

The vote comes amid stalled negotiations between bailed-out Greece and its international creditors.

Conservative Prime Minister Antonis Samaras is backing former European Union commission Stavros Dimas for the presidency.

Dimas is the only candidate, but to win he needs support from at least 25 independent or opposition lawmakers to avoid a snap general election. So far, fewer than 10 have declared their support.

If Dimas falls short on Wednesday, a second round is scheduled for Dec. 23 and a third on Dec. 29, when 180 votes are needed.

If the third round fails, Parliament would be dissolved and early elections called.