The two contenders for the French presidency entered the final day of campaigning Friday, with opinion polls giving challenger Francois Hollande the edge over President Nicolas Sarkozy.

Sarkozy is holding a rally at lunchtime in the western Vendee area at lunchtime, while Hollande will address supporters later Friday in Moselle, to the east of France.

Campaigning ends at midnight Friday ahead of Sunday's runoff vote for the presidency.

It has been dominated by concerns over the economy, as France struggles to overcome low growth and 10% unemployment, and immigration issues.

A final opinion poll conducted by CSA for CNN affiliate BFM-TV and other outlets ahead of the second-round vote gives Hollande a 6-point lead over his rival, with 53% support to 47% for Sarkozy.

Hollande, speaking to French radio station RTL early Friday, suggested Sarkozy had miscalculated his Socialist rival's strength in the run-up to the vote.

"I have never underestimated Nicolas Sarkozy," he said. "I challenged his policies, his choices, his behavior, his ways, even during these last hours. But I know his energy, his strength of conviction and his talent as a debater.

"But, where he made a mistake was that he underestimated me. And in politics, he who underestimates (his opponent) overestimates himself and thus makes an error in judgment."

The two traded insults Wednesday night in the only televised head-to-head debate of the campaign.

Sarkozy labeled Hollande a liar and a "little slanderer," while the Socialist accused the president of shirking his responsibilities, cronyism and favoring the privileged over France's poor.

Both Sarkozy, of the center-right UMP party, and Hollande have been working hard to reach out to France's undecided voters in the two weeks since the first-round vote.

Centrist candidate Francois Bayrou on Thursday said he would vote for Hollande, but urged his supporters to vote according to their conscience. He took 9% of the vote in the first-round ballot on April 22.

Speaking on French radio Europe 1 Friday, Sarkozy questioned the logic of Bayrou's decision.

"He said that after much thought, he was voting Francois Hollande, and he added that this will lead to bankruptcy in February. Is that logical? It's hard to find coherence," he said.

"What's important is that almost all elected officials who support Bayrou joined me and I thank them for that. The others are free to express their own choice with their vote."

Marine Le Pen, who as leader of the far-right National Front party attracted nearly a fifth of the first-round votes, has not endorsed either candidate.

Saying she would leave her own voting slip blank on Sunday, Le Pen told supporters to vote "with your soul and your conscience."

In the April 22 ballot, Hollande received 28.6% of the vote, slightly ahead of Sarkozy's 27.2%. Le Pen, who has called for sharply curbing immigration, received 18% of the vote.

If elected, Hollande would be France's first left-wing president since Francois Mitterrand left office in 1995. Sarkozy has been president since 2007.