French police braced for violence on Sunday as a mass demonstration against a new gay marriage law kicked off in Paris amid warnings hardliners were expected to mingle with protesters and cause trouble.
One of President Francois Hollande's campaign pledges, the bill allowing same-sex marriage and adoption was voted into law on May 18 following months of protests across a country that has been bitterly divided over the issue.
While rights groups have hailed the move, opponents have vowed to fight on and tens of thousands of people converged on the capital Sunday for a last-ditch show-of-force.
"Yes to human dignity", one banner read as protesters blowing whistles and horns began the march. One man dressed in black, holding a scythe and wearing a mask of Hollande stood behind a coffin in which lay a mannequin dressed as Marianne, the emblem of France.
Some 4,500 security personnel have been mobilised for the protest, for which people come from across France in specially chartered trains and buses. Two million leaflets advertising the march have been distributed.
Interior Minister Manuel Valls has warned that so-called "ultras" -- many of them far-right nationalists -- are expected to infiltrate the protest and cause unrest, and advised parents not to bring their children with them.
Many in the protest had however ignored the warning, bringing their children as others had in previous demonstrations.
"We keep hearing about a far-right movement, I can see only families here," said one man called Raoul, who came from the city of Dijon, some 300 kilometres (186 miles) away.
But already on Saturday, trouble began when protesters chained themselves to metal barriers they placed in the middle of the busy Champs-Elysees street, some firing smoke cannisters while dozens more assembled on the pavement.
Police detained a total of 50 people and also seized a van packed with masks, banners and smoke bombs.
Supporters and opponents of the bill began protesting last autumn when it was adopted by the cabinet, and have continued to do so at regular intervals throughout the country during the legislative process.
But as the bill neared the final stages of approval, anti-gay marriage demonstrations were often disrupted by radicals and at times descended into violence.
Fears of unrest on Sunday have also been compounded by violence that erupted earlier this month during celebrations marking football club Paris Saint-Germain's league victory that saw tourists attacked and shop and car windows smashed.
Sunday's protest is organised by the "Manif Pour Tous" -- the ringleaders of the movement -- and has been divided into three, separate processions that will converge on the Invalides esplanade in central Paris.
A separate rally was due to take place near the Paris opera, protesting the same issue but organised by conservative Catholic group Civitas.
The leader of the right-wing UMP party Jean-Francois Cope is taking part in the main demonstration, as are members of the far-right National Front.
Frigide Barjot, the leader of the "Manif Pour Tous" movement, has meanwhile decided not to attend, saying she has been the subject of death threats from far-right activists.
France is the 14th country to legalise same-sex marriage, an issue that has divided opinion in many other nations too.
In Brazil, for instance, tens of thousands of evangelical Christians marched in Rio de Janeiro on Saturday protesting a recent legal ruling allowing gay marriage.
But according to a survey published Sunday in the Journal du Dimanche, nearly three-quarters of French people are tired of the anti-bill protests and think they should stop.