Police set off tear gas to disperse them.
On the campaign trail, the race was narrowing ahead of Sunday's vote, with the pack closing behind frontrunners Macron and Le Pen.
If, as expected, no single candidate exceeds 50% of the vote, the two candidates with the most votes will head to a second round of voting.
The 26-year-old says, "We saw Trump, we saw Brexit.so I'm mistrustful".
Le Pen dropped by 2.5 percentage points to 22.5 percent of voting intentions since early April, and Macron fell 2 percentage points to 23 percent in the first round.
Opponents of Le Pen and her anti-immigration National Front party also skirmished with police outside a Paris rally this week.
The protesters also carried banners and placards that read "Marseille against the National Front" - Le Pen's eurosceptic party - "Migrants Welcome, Fascists get out!", and "The Extreme Right, you can't fight at the ballot box".
Extremism concerns shook France's presidential campaign Tuesday as authorities announced arrests in what they said was a thwarted attack and candidates urged tougher counterterrorism efforts for a country already under a state of emergency.
He said ten of the 11 candidates wanted to take France back to a "fantasy of the past". She supports banning "conspicuous religious symbols" in public places because "the Muslim religion has arrived in our country like a tidal wave and radical Islam has begun to apply pressure by means of the veil". Only the two top-getters will advance to the runoff on May 7. The hard left candidate's proposals have seen him propose a 100% income tax on incomes twenty times and above the median income.
French Socialist presidential candidate Benoit Hamon, left, poses for a selfie with supporters during a last-ditch rally and concert in Paris, Wednesday, April 19, 2017.
President Francois Hollande called the arrests "remarkable" and praised police for stopping the planned terror attack.
"The fact that the two individuals were arrested in Marseille as Marine Le Pen was preparing to hold a meeting the following day is perhaps not a coincidence", a member of her entourage said.
As the first round campaign draws to a close, security details protecting the candidates have been bolstered after intelligence services detected an imminent threat.
She assailed recent governments for failing to stop extremist attacks in recent years and warned on BFM television that "we are all targets".
Addressing almost 5,000 flag-waving supporters in the southern city of Marseille, where two Frenchmen were arrested Tuesday on suspicion of planning an attack on the election, the National Front (FN) leader said: "I have been denouncing this awful poison of Islamic terrorism since I launched my campaign ... and none of my rivals are willing to debate the subject".
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