At least 45,000 people have attended the last big rally against same-sex marriage and adoption in Paris before the bill is expected to become law, BBC News said.

Rejecting the police estimate of the turnout, organisers said 270,000 people had attended the march.

The event unfolded peacefully despite fears of clashes after incidents at previous protests this year.

At least 3,500 people joined a rival march in support of the bill, which is likely to be passed on Tuesday, April 23.

President Francois Hollande and his ruling Socialist Party have made the legislation their flagship social reform since being elected nearly a year ago.

Hollande has been struggling with the lowest popularity ratings of any recent French president, with his promises of economic growth so far failing to bear fruit and unemployment now above 10%.

Opinion polls have suggested that around 55-60% of French people support gay marriage but only about 50% approve of gay adoption.

The anti-gay marriage lobby, backed by the Catholic Church and conservative opposition, argues the move will undermine an essential building block of society.