Nicolas Sarkozy has sought to play down the importance of the vote
Nicolas Sarkozy's centre-right UMP party appears to be heading for defeat in French regional elections.
Initial results suggest the opposition Socialist party has taken a strong lead in the first round of voting.
The outcome will be a major blow for Mr Sarkozy in the last nationwide poll before presidential and parliamentary elections due in 2012.
The far-right National Front looks to have done better than expected, with up to 12% of the vote.
Sunday's election took place with President Sarkozy's popularity rating at an all-time low and unemployment at 10%.
The French leader had sought to play down the importance of the vote, insisting it was only about regional issues.
But many voters used it to signal their disapproval of the president and his government, says the BBC's Emma Jane Kirby, in Paris.
As well as the fallout from the economic crisis, a range of unpopular planned reforms appear to have cost the governing party.
Turnout for the ballot was also poor. The abstention rate was put at some 52%, a record for a regional election.
President Sarkozy did not comment on Sunday night, but Prime Minister Francois Fillon insisted the vote was not over.
Near complete results suggested the Socialists were likely to emerge as the largest single party, and that the centre-left and Greens would get more than half the vote.
The leader of the Socialists, Martine Aubry, said the result was a blow to President Sarkozy's government.
"By this vote the French people have sent a clear and strong message of refusal to a France that is divided, anguished and weakened," she said.
Le Pen triumphant
The Socialist party is deeply divided at national level, but remains strong in the regions.
It already controls 20 out of 22 regional councils in the country and now looks likely to make further gains in the final vote next Sunday.
FRANCE'S ELECTORAL CALENDAR
May-June 2007: Presidential and parliamentary elections see Sarkozy elected president and UMP victory
March 2010: Regional elections provide key half-term test
May-June 2012: Next presidential and parliamentary elections
National Front leader Jean-Marie Le Pen appeared on national television after the vote, holding a poster banned by a court that read: "No to Islamism."
The 81-year-old politician called on voters to back the party again in round two, saying his party was "combative and capable of rebuilding this country, which is in a horrible state."
His party effectively tied for third-place nationally with Europe Ecologie.
The National Front's surprising performance comes against the background of social and racial tensions after the government's public debate on national identity.
Some 44 million voters were registered to elect 1,880 councillors from party lists to control regional budgets on transport, education and economic development.