Vincent Autin and Bruno Boileau said "I do" on Wednesday in France's first official gay marriage, as hundreds of guests and journalists looked on in the highly emotional ceremony.

"I now pronounce you united in marriage by law", Helene Mandroux, the visibly moved mayor of the southern city of Montpellier, told the couple to general applause, as Frank Sinatra's song "Love and Marriage" filled the room.

The high-profile ceremony, also attended by the Socialist government's spokeswoman Najat Vallaud-Belkacem, is the apex of months of huge divisions in France over a bill allowing same-sex marriage and adoption.

The bill was finally signed into law on May 18 to the cheers of supporters, but opponents have vowed to fight on and tens of thousands converged on Paris Sunday for a demonstration that ended in violence.

Autin, 40, made a short speech after the ceremony thanking supporters and his family, frequently breaking down in tears. "Love yourselves, let's love ourselves, because it's important," he said.

Mandroux then read out a letter by Jack Lang, a former culture and education minister who is gay. "Your happiness delights me... Here's to love, here's to life."

The ceremony took place under police surveillance, but no major incidents were reported.

Supporters of same-sex marriage had gathered outside the town hall in Montpellier where the marriage took place, as had some opponents who let off several flares.