PARIS -- Paris riot police fought back crowds who pushed their way onto Paris' landmark Champs-Elysees avenue as part of a huge protest against a draft law allowing same-sex couples to marry and adopt children.

Hundreds of thousands of people -- conservative activists, children, retirees, priests -- converged on the capital Sunday in a last-ditch bid to stop the bill, many bused in from the French provinces.

The lower house of France's parliament approved the "marriage for everyone" bill last month with a large majority, and it's facing a vote in the Senate next month. Both houses are dominated by French President Francois Hollande's Socialist Party and its allies.

Sustained protests led by opposition conservatives in this traditionally Catholic country have eroded support for the draft law in recent months, and organizers hope Sunday's march will weigh on the Senate debate.

The first few hours of the protest were peaceful. But as it was meant to be winding down, about 100 youths tried to push past police barricades onto the Champs-Elysees, the avenue that cuts through central Paris and draws throngs of tourists daily. In an indication of the sensitivity of the issue, protesters had been barred from marching on the Champs.

Police officers wrangled with the youths and then fired tear gas to force them back. Gaining momentum, more and more protesters took side streets to reach the avenue, blocking a key intersection on the route to the president's Elysee Palace.

Police fired more tear gas but were unable to block the crowds from spilling onto the avenue.

"Hollande, Resignation!" the protestors chanted, before breaking into the French anthem, "La Marseillaise."

The demonstrations have become outlets for anger and disappointment in Hollande's presidency.

An official with the Paris police headquarters said two people were arrested and no injuries were reported. The police official was not authorized to be publicly named in accordance with police policy.

The official estimated that 300,000 people took part in Sunday's march, slightly less than a similar march in January. Organizers estimated more than 1.2 million people took part in Sunday's march, more than in the January protest.

Polls indicate a shrinking majority of French voters back gay marriage, which is legal in about a dozen mostly European nations and some U.S. states. But polls show French voters are less enthusiastic about adoption by same-sex couples.

Frigide Barjot, the stage name of an activist who has led protests against the bill, insisted the anti-gay marriage movement wasn't a lost cause. "It's the second round, sir. It's not the last battle."