Several hundred thousand opponents of same-sex marriage took to the streets of the French capital to demonstrate against the reform, which was signed into law by President Francois Hollande last week.

While the rally was peaceful throughout much of the day, police said they arrested 96 hardline opponents to the gay marriage law.

Police said those arrested were detained for refusing to disperse or for occupying private property.

Large park grounds around the Les Invalides monument were full of protesters waving pink and blue flags, while far-right activists hung a banner on the ruling Socialist Party headquarters urging Hollande to quit.

The protests, which began as a grassroots campaign strongly backed by the Roman Catholic Church, have morphed into a wider movement with opposition politicians and far-right militants airing their discontent with Hollande.

Although they have failed to block gay marriage, the protesters hope their renewed show of force will help stop or slow down further laws some socialists want allowing assisted procreation and surrogate motherhood for gay couples.

Jean-Francois Cope, leader of the opposition UMP party, marched in the demonstration and urged young protesters to join his party to keep up pressure on the left-wing government.

"The next rendezvous should be at the ballot boxes for the municipal elections," he said, referring to local polls due next year where conservatives hope to profit from the protest movement's unexpectedly strong mobilisation.

Once the bulk of protesters had gone home, clashes erupted between hardliners wielding sticks and riot police, filling the Invalides Esplanade with tear gas.

Police said 150,000 marched on Sunday while protest organisers said a million people took part.