PARIS: The battle to decide the Socialist candidate for the French presidential election will be whittled down to two in a primary vote on Sunday in which ex-prime minister Manuel Valls faces an outside risk of failing to make it to the party runoff.

Candidates who are to the left of Valls, such as former education minister Benoit Hamon and ex-economy minister Arnaud Montebourg, are nipping at his heels in the polls as the pro-business Socialist has struggled to defend his government's record.

Seven candidates from the Socialists and their allies are taking part in the first round of the primary, with polls closing at 1300 EST. A runoff will then be held on January 29 to pick a candidate for the two-round presidential election on April 23 and May 7.

Regardless of who wins this primary, polls indicate that the Socialist candidate has next to no chance of making it into the runoff in the presidential election.

One of the dominant forces of French politics for decades, the Socialist party has seen support evaporate during Francois Hollande's presidency as he has struggled to turn the economy around and alienated left-wing voters with his economic policies.

The Socialists' choice of presidential candidate will be key for the chances of popular independent Emmanuel Macron, who is attracting middle ground voters who Valls also appeals to.

Polls indicate conservative former prime minister Francois Fillon is most likely to emerge as the winner of the presidential election in a runoff against far-right National Front leader Marine Le Pen.

Fillon's program includes cutting business taxes, relaxing labor laws and scrapping the 35-hour working week in an attempt to boost growth, while also cutting half a million public sector jobs as part of a drive to shrink the state sector.

But Macron, a youthful and charismatic one-time investment banker, has been gaining ground and could make it into a presidential runoff against Fillon if a leftwinger like Montebourg or Hamon wins the Socialist nomination.

A poll last week saw Valls, who stepped down from government last month, coming out on top in both rounds of the primary vote with 37 percent in the first round.

However, his lead narrowed after Hamon made a stronger impression in a series of televised debates, with a proposal for monthly income support payments for all.

Hamon and Montebourg were kicked out of the Socialist government led by Valls in 2014 for criticizing its economic policies, which they criticized as too favorable to business.