Former Economy Minister Arnaud Montebourg was seen as marginally winning the first French left-wing primary television debate on Thursday, raising the prospect of a tight race to select the left's candidate for the 2017 presidential election.

The winner of the primary at this stage has little prospect of topping the April-May presidential vote with all the leading candidates — conservative Francois Fillon, far-right National Front leader Marine Le Pen and independent former Economy Minister Emmanuel Macron — all well ahead.

However, polls show that the result of the primaries is likely to impact Macron's chances, with Macron possibly reaching the presidential runoff depending on which candidate the left picks for the party ticket.