President Emmanuel Macron promised to put the environment at the heart of his government if he is re-elected this weekend, in a speech in southern France on Saturday designed to appeal to young and green-minded voters.
Macron held a major rally in the port city of Marseille while his rival, far-right leader Marine Le Pen, visited a village west of Paris.
Polls show Macron stretching his lead over Le Pen, with a fresh survey on Saturday by Ipsos Sopra/Steria suggesting that Macron would triumph with 55.5 percent versus 44.5 percent for Le Pen.
"I hear the anxiety that exists in a lot of our young people. I see young people, adolescents, who are fearful about the future of our planet," Macron told the rally.
He acknowledged the "powerful message" sent in the first round of elections on April 10, when nearly eight million voters backed hard-left candidate Jean-Luc Melenchon and his ecology-heavy programme.
"It's up to us to react and up to us to take action," Macron said.
As well as promising to make France "the first major nation to abandon gas, oil and coal", Macron said he would appoint a prime minister who would be formally tasked with "ecological planning".
He also promised new investments in renewable technologies, energy-saving residential renovations and organic food production, while pledging crackdowns on air pollution and single-use plastics.
The speech was a clear pitch to the young and left-wing voters who backed Melenchon and Greens nominee Yannick Jadot in the first round who will be crucial in the second round on April 24.
The idea of a prime minister tasked with "ecological planning" was first proposed by Melenchon.
Macron accused Le Pen of being "a climate change sceptic", attacking her for proposing to dismantle wind turbines, which she views as costly, inefficient eyesores.
Surveys show the environment is one of French voters' priorities, but it has been overshadowed during the election campaign by the war in Ukraine and the spiralling cost of living.
Several hundred activists from the Extinction Rebellion climate activist group blocked a main road in the centre of Paris on Saturday to denounce the "inaction" of political leaders.
"This is the only way of ensuring that everyone talks a bit about climate change," said Antoine, a young Extinction Rebellion activist who declined to give his surname.
Le Pen meanwhile was touring the village of Saint Remy-sur-Avre, about an hour and half's drive west of Paris, where she came top in the previous weekend's first round.
After hearing complaints about the loss of hospital beds and bus services locally, she promised to "govern the country like a mother, with common sense" and to defend "the most vulnerable".
She has sought to moderate her image during campaigning this year, stressing her proposed solutions to rising living costs rather than her usual topics of immigration and Islam.
Rallies backed by trade unions against the far-right were staged in major cities on Saturday. Nearly 23,000 people turned out for the demonstrations, according to interior ministry estimates: 150,000 according to the rallies' organisers.
Le Pen faced repeated questions last week about her proposed ban on the Islamic headscarf in public places, which she has said will be punished with fines by the police.
The 52-year-old mother-of-three admitted on Saturday it was a "complex problem" and would be discussed by parliament if she won.
But "we need to resolve the problem of women who are obliged to wear it under pressure from Islamists", she said.
She has also sought to appeal to left-wing voters, who she will need in order to defeat Macron.
"We are speaking to all the French," she told a rally in the southern city of Avignon on Thursday evening. "We hold out a firm hand but one of friendship and respect."
Although both candidates claim to have strong environmental programmes, they have clear differences in foreign policy, attitudes to immigration, and the economy.
Eurosceptic Le Pen wants to wind back France's commitments to the EU and has proposed closer ties between Western military alliance NATO and Russia once the war in Ukraine is over.
Macron and Le Pen are set to meet in a crucial head-to-head debate on Wednesday evening which has proved crucial in swaying voters in the past.
Meanwhile the investigative website Mediapart reported Saturday that the EU's anti-corruption office OLAF had delivered a report to French prosecutors last month accusing Le Pen of having fraudulently used money she received when she was a European deputy between 2004 and 2017.
