Nicolas Sarkozy's approval ratings have fallen in recent months
President Nicolas Sarkozy's centre-right UMP party has suffered a heavy defeat in French regional elections.
The Socialist-led opposition alliance took about 54% of the vote with the UMP on 36%. About 51% of voters turned out.
Prime Minister Francois Fillon acknowledged the defeat, admitting the left's "success". A cabinet reshuffle is expected.
The results leave the UMP in control of only one of France's 22 regions - Alsace in the east.
These elections are the last major electoral test in France before the presidential election in 2012.
"I assume my share of the responsibility", Mr Fillon said.
Mr Fillon is due to meet Mr Sarkozy on Monday, but a senior official has dismissed speculation that the prime minister would offer to resign.
Opposition leader Martine Aubry was quoted as saying the results expressed the French people's "rejection of the politics of the president and the government".
With Mr Sarkozy's approval ratings at an all-time low, the poor election results have prompted the president to plan a modest reshuffle of the governmen, said his chief of staff Claude Gueant .
One poll suggests that 57% of people would like to see a change of government after the regional polls.
However the poor results may make the French leader far more cautious about pushing through his comprehensive programme of reforms which has already clearly cost him votes, the BBC's Emma Jane Kirby reports from Paris.
Many people are angry that Mr Sarkozy's election promises - to make ordinary people richer and to make France more competitive - have failed to come good, our correspondent says.
With three million people currently out of work, France is now suffering its highest level of unemployment in decades, while a series of unpopular reforms has prompted numerous strikes and protests over recent months.
Mr Sarkozy himself has suggested the possibility of a pause in the pace of reforms after the elections.
Although the elections are meant to be about regional issues, such as public transport, other factors like high unemployment and resentment over plans to reform the judicial and pension systems have prompted many French people to use the ballot to punish the government.
In the first round ballot less than half of France bothered to vote. That cost President Sarkozy's right-wing party dearly.
The UMP won just over a quarter of the vote, while the opposition Socialists, combined with other leftist parties, took 50%.