France's far right National Front has won more support than any other party in the first round of regional elections, according to polling agency projections.
It is a new boost for Marine Le Pen's anti-immigration strategy and a fresh blow to President Francois Hollande's Socialists.
The projections put National Front candidates on top so far in six of France's 13 newly-drawn regions. But Sunday's voting was only a first round, and some mainstream voters may steer away from far right candidates in the decisive December 13 run-off.
The elections took place in an unusually tense security climate just over three weeks after deadly attacks on Paris - a climate expected to favour conservative and far right candidates. It is the last election before France votes for president in 2017 and a gauge of the country's political direction.
Voters are choosing leadership councils for the regions, and had the choice of several parties in the first round. Polling agencies Ifop, OpinionWay and Ipsos projected that the National Front won between 27 and 30% support nationwide.
The polling projections estimated the percentage of votes for different parties, not the number of seats they are expected to win on France's regional councils. The number of seats will be determined in next Sunday's run-off, which pits the leading parties in each region against each other.
Former president Nicolas Sarkozy's conservative Republicans party and its allies were projected to come second in the national vote at around 27%. The Socialists, who currently run nearly all of the country's regions, were projected to come in a weak third place, with between 22 and 24%, followed by a smattering of mainly leftist groupings.
The big question for the run-off is whether supporters of Republicans, Socialist, and smaller candidates will rally together to keep the National Front from winning control of any of the regions. The party, long considered a pariah, has never had such significant political power.
The National Front is hoping the regional elections will consolidate political gains Ms Le Pen has made in recent years, and strengthen its legitimacy as she prepares to seek the presidency in 2017.
The National Front "is the only (party) that defends an authentic French republic, a republic with only one vocation: the national interest, the development of French employment, the conservation of our way of life, the development of our tradition and the defense of all the French," Ms Le Pen said in Lille.
The Islamic State (IS)-inspired Paris attacks on November 13 that killed 130 people and a Europe-wide migrant crisis this year have shaken up France's political landscape.
The arrival of hundreds of thousands of migrants in Europe and the exploits of IS have bolstered the discourse of the National Front, which denounces Europe's open borders, what it calls the "migratory submersion" and what it claims is the corrupting influence of Islam on French civilisation.
Ms Le Pen is campaigning to run the northern Nord-Pas-de-Calais-Picardie, which includes the port city of Calais, a flashpoint in Europe's migrant drama. Her young niece, Marion Marechal-Le Pen, is running to lead the southern Provence-Alpes-Cote d'Azur region.
Projections showed the National Front lists with around 40% first-round support in both regions, a good 15% ahead of second-place Republicans. Socialist leader Jean-Christophe Cambadelis called for his party to withdraw from the run-off in both races in hopes of keeping the National Front from winning.
Voters left and right joined together to keep Marine's father Jean-Marie Le Pen from winning a presidential run-off in 2002. However, Marine Le Pen has worked to undo its image as an anti-Semitic party and has lured in new followers from the left, the traditional right and among young people.
"The verdict of the French people tonight is clear," Mr Sarkozy said last night. "We must hear and understand the deep exasperation."
He said his party should refuse to ally with any National Front candidates or to pull out of any races in the second round. A victory for National Front ideas "would dramatically aggravate France's situation and create conditions of dangerous disorder", he said.
Socialist prime minister Manuel Valls and the conservative-leaning national business lobby issued a public appeal this week to stop the National Front's march towards victory.
Mr Hollande's Socialist Party, which currently runs nearly all of France's regions, has seen its electoral support shrivel as the government has failed to shrink 10% joblessness or invigorate the economy.
Many political leaders urged apathetic voters to cast ballots as a riposte to fundamentalists targeting democracies from France to the US.
First-time voter Eli Hodara, an 18-year-old Paris student, expressed hope that more young people would turn out, saying: "I think it is important to vote even if one leaves the ballot blank."