Tens of thousands of people protested against France's new gay marriage law in central Paris today.

The law came into force over a week ago, but organisers decided to go ahead with the long-planned demonstration to show their continued opposition as well as their frustration with President Francois Hollande, who had made legalising gay marriage one of his keynote campaign pledges in last year's election.

Marchers set off from three separate points across Paris, and by early evening they filled the Invalides esplanade just across the Seine River from the Champs Elysees.

Police estimated around 150,000 people took part in the demonstration, but march organisers claimed on their Twitter account that more than one million people did.

A similar protest in March drew about 300,000.

Around 5,000 police were on duty because previous anti-gay marriage protests have seen clashes between far-right protesters and the police.