The Socialists hold a primary contest for the party's candidate in the 2017 presidential election. President Francois Hollande will not be one of the rivals of frontrunner Manuel Valls in the crowded field.
Hollande decided not to run because of his record-low approval ratings.
Ex-prime minister Valls is widely expected to win the first round in the field of at least 12 candidates.
If no candidate wins 50 per cent of the vote, a second round will be held on Jan 29 between the two candidates with the most votes.
The Bloomberg news service reports that disenchantment with Socialist government policies is so high that even Hollande alternatives, such as Valls or Lille Mayor Martine Aubry, could lose to centre-right candidate Francois Fillon or far-right party leader Marine Le Pen in the first round.
The Socialists' chances would improve if the left-leaning parties came together to field a single candidate, but the prospects for agreement are considered to be low.
Date written/update: 2016-12-08