The two rivals in France's presidential race have traded accusations at the start of the last week of campaigning.
Far-right candidate Marine Le Pen lambasted pro-EU centrist Emmanuel Macron as a "candidate of continuity".
Mr Macron said he would fight "until the last second" against Ms Le Pen's ideas "of what constitutes democracy".
Meanwhile, clashes broke out between police and protesters on the sidelines of a traditional May Day labour march in Paris.
Four officers were hurt when masked demonstrators threw petrol bombs at police who responded with tear gas, authorities said.
The violence happened near Place de la Bastille as the march, led by three trade unions, headed towards another square.
Reacting to the violent scenes, Ms Le Pen said on Twitter: "This is the sort of mess... that I no longer want to see on our streets."
Ms Le Pen trails Mr Macron in the polls by about 20 percentage points ahead of Sunday's decisive second round.
She has sought to modernise the National Front (FN) in recent years and at her rally in Paris, she called herself the candidate of change, belief and action.
She launched a full-throttled attack on Mr Macron, calling him the candidate of "a morbid continuity, littered with the corpses of jobs transferred offshore, the ruins of bust businesses, and the gaping holes of deficit and debt".
"Emmanuel Macron is just [current President] Francois Hollande, who wants to stay and who is hanging on to power like a barnacle," she told a rally in Villepinte, a suburb north of the capital.
Mr Macron, an independent and leader of the recently created En Marche! movement, has sought to portray Ms Le Pen as an extremist.
"I will fight up until the very last second not only against her programme but also her idea of what constitutes democracy and the French Republic," he told reporters.
Addressing a rally later in Paris, he told supporters that the future of France, of Europe "and of a certain concept of the world", was at stake in the election.
Mr Macron earlier told the BBC that the EU must reform or face the prospect of "Frexit" - the French equivalent of Britain's Brexit.
Ms Le Pen, 48, has capitalised on anti-EU feeling, and has promised a referendum on France's membership.
She has won support in rural and former industrial areas by promising to retake control of France's borders from the EU and slash immigration.
Although five major unions have urged their members not to vote for Ms Le Pen, only two have expressed their support for Mr Macron.
Also on Monday, Ms Le Pen's estranged 88-year-old father and the founder of the FN was at a rally by the statue of Joan of Arc, a long-time symbol of patriotism for the FN.
This is where Jean-Marie Le Pen traditionally held his May Day rallies but this year's event was attended by only a couple of hundred of the party's old guard, BBC Paris correspondent Hugh Schofield reports.