Voters punished France's centre-right government for its poor economic record and lack of direction in Sunday's first round of regional elections.
Exit polls forecast significant gains by the left, led by the opposition Socialist party, amid a higher-than-expected voter turnout to elect new councils in the 22 metropolitan regions and four overseas territories.
The abstention rate was 39 per cent among France's 37m electorate - almost four percentage points lower than in the 1998 regional elections.
Commentators seized on the larger number going to the polls as evidence that the elections had been turned into a referendum on the Raffarin government's record after nearly two years in office. The government's weak performance was expected to increase pressure on President Jacques Chirac to consider a major reshuffle, including appointing a successor to premier Jean-Pierre Raffarin.
However, Mr Chirac was not expected to make any move until after the second round of voting next Sunday.
Exit polls gave the mainstream parties of the left, led by the Socialists, 40 per cent of the vote against 34 per cent for the centre right, dominated by the ruling UMP. The extreme right National Front vote held up well at about 17 per cent but hard left support fell back compared with the 2002 presidential and general elections.
The left-wing opposition has sought to turn the regional elections, in theory based on local issues, into an anti-government vote, allowing them to recoup some of the ground lost in the 2002 polls.
Opposition parties believe they have profited from the knock-on effect of of last Sunday's surprise Socialist victory in Spain.
The UMP, formed two years ago from a merger of the main right-wing parties in France, has forged close ties with Spain's ousted Popular Party.
The two-round poll will not affect the UMP's overwhelming parliamentary majority. But a strong protest vote against the government would increase internal divisions which came to the fore after January's conviction on corruption charges of Alain Juppé, the party leader and Mr Chirac's heir apparent.
A total of 19 members of the government were standing for office, which helped to turn each regional battle into a broader national contest. Mr Raffarin had been increasingly defensive in the run-up to the elections, often clumsily seeking to use the heightened terrorist threat as a rallying call for his UMP party.
The electoral rules have been changed allowing only those parties or alliances with 10 per cent of the vote to go through to the second round.
Although the National Front looked set to take part in 19 of the 22 run-offs, splitting and thus weakening the ruling UMP's chances of victory by creating three-cornered contests, the extreme right was unlikely to gain control anywhere.
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