The head of the French Socialists admitted his party faced
Projections after the first round of the parliamentary vote showed the party falling to 15-40 seats in the new national assembly from 277 currently. A second round of voting will take place next Sunday.
If confirmed, the party's collapse would be even worse than in 1993 when it fell to 56 seats from 278 at the latter end of Socialist president Francois Mitterrand's second term.
The results were "marked by an unprecedented retreat of the left as a whole and the PS (Socialist Party) in particular," the party's head Jean-Christophe Cambadelis said in comments after the first projections were published.
Sunday's results underline the emphatic rejection of the outgoing Socialist government headed by ex-president Francois Hollande, who hit record levels of unpopularity during his five-year term as leader.
Julien Dray, a senior Socialist leader, said it was "a profound political crisis. Firstly we'll have to see the second round... we need to keep fighting and afterwards we will need to rework completely what was the Socialist identity."
The party has already raised the possibility of having to sell its headquarters in central Paris as it haemorrhages donations and public subsidies which are essential for keeping it afloat.
Projections on Sunday indicated that President Emmanuel Macron's centrist party Republique en Marche (Republic on the Move, REM) and its allies were on course for a huge majority of 390-445 seats in the 577-member National Assembly.
Macron served as economy minister in the previous Socialist government, but fell out with the party's leaders over his desire to push pro-business and market-friendly reforms.
The 39-year-old was briefly a Socialist party member in his twenties, but started his En Marche movement last April in a bid to redraw French politics around a new centrist force at the expense of France's traditional parties.