France's prime minister, Manuel Valls, has resigned to declare himself a candidate for the presidency in an attempt to save the Socialist Party from a humiliating exit from elections next spring.

Mr Valls, 54, a reformist, launched his bid to win party primaries just four days after François Hollande announced he would not seek re-election next May.

Speaking in Evry, the gritty Paris suburb where he was long mayor, he said: "Yes, I'm candidate for the presidency."

"I will leave my post (of prime minister) tomorrow."

Mr Valls, who served as prime minister for two years, hopes to prevent leftist former cabinet rebels, notably Arnaud Montebourg, self-styled champion of "Le Made in France", from winning the candidacy next month.

The father of four who is married to Anne Gravoin, a glamorous concert violinist who was present in the Evry town hall where the pair were wed, is tipped to narrowly win the party nomination against a field of seven candidates, polls suggest.