HUNDREDS of thousands of protesters have flooded the streets of Paris in protest at government plans to legalise gay marriage and adoption.

With the proposed legislation due to go before parliament at the end of this month, opponents travelled from all over France for a demonstration supported by leaders of the mainstream centre-right opposition, the Catholic Church and France's five-million-strong Muslim community.

Organisers of the 'demo for all' (a reference to the government's billing of its legislation as 'marriage for all') estimated attendance at 800,000, but the police suggested a figure of around 340,000 was nearer the mark.

The protesters hope their show of strength will put pressure on President Francois Hollande to review the plans or agree a referendum.

But the Socialist leader has made it clear he has no intention of dropping a promise he made in his election manifesto last year and to which he is personally committed.

Hollande is already pencilled in to attend one of France's first gay marriages once the legislation is enacted later this year.

Despite months of protests, opinion polls have shown consistently that most voters support the right of homosexual couples to marry and a narrower majority favour granting them adoption rights.

The slim prospect of success did not appear to dampen the spirits of the protesters however as giant marches converged near the Eiffel Tower on Sunday after setting off from three different starting points.

Many of the protesters were accompanied by children, some of whom brandished placards exclaiming: "Born of a man and a woman." A more light-hearted banner proclaimed: "There are no eggs in the testicles."

Jacques Julien, 70, who had travelled from the Haute Loire region of central France, said he had voted for Hollande but disagreed with the Socialist president's approach.

"A man and a woman, that is the basis of the family," he said. "I'm saying out loud what many people on the left think privately."

The movement against gay marriage has given France a new celebrity in the form of its public face, Virginie Tellenne, a Parisian socialite who goes by the name of Frigide Barjot.

Her assumed name - a play on the name of French film star Brigitte Bardot, a sex symbol in the 1960s - translates as Frigid Loony.

"The president must listen to us," Barjot said. "He must put this law on hold."