France's bitter debate over gay marriage is set to reach a potentially explosive climax on Sunday, two days before a bill legalising same-sex unions is due to be finally approved.

Opponents of the reform have been urged to take to the streets of Paris in a last-ditch show of their hostility to the reform after a week of regular and sometimes violent protests.

"There are only a few days left and we are not going to abandon the streets now," one of the organisers of Sunday's demonstration, Alberic Dumont, told AFP.

Tens of thousands are expected to turn out, although organisers admit they are unlikely to see a repeat of a huge demonstration in March that was attended by more than 300,000 people.

A parallel demonstration by supporters of the right of gays to marry and adopt children has also been called for Sunday.

A final, decisive vote on the bill is scheduled to take place on Tuesday and, in the countdown to that, there have been daily protests in Paris and other cities.

The tensions on the streets were mirrored in France's National Assembly, where the final debate on the bill was marred by unprecedented scuffles between deputies on opposite sides of the argument in the early hours of Friday.

Opponents have accused the government of rushing the bill through its final legislative stages by implementing a fast-track measure that has limited debate to 25 hours.

And while the end of the debate at around 7am (0500 GMT) on Friday was hailed as a "historic moment" by the Socialist speaker of the lower house National Assembly, the opposition UMP claimed the government had made a mockery of the parliamentary process.

Meanwhile, opponents continued to protest in Paris and other cities in France, with 75 people detained Thursday -- three of whom have been accused of violence against police and theft.

On Wednesday, demonstrations also turned violent, with two journalists attacked, their equipment destroyed, and cars vandalised.

News of a fresh attack on a gay bar also emerged, with the manager and client of an establishment in the southwestern city of Bordeaux assaulted overnight on Wednesday by two people who also smashed bottles and glasses.

The attack happened on the same night as a similar incident in the northern city of Lille, where three employees of a gay bar were injured in an attack by four men who smashed the building's windows.

Yohan Jerczynski, the owner of the bar, denounced the current climate of "insecurity" on TV channel Canal Plus, saying he had never had any problems in his bar in 14 years. Three suspects were to face a fast-track trial on Friday.

President Francois Hollande has condemned the "homophobic" violence in France, and Interior Minister Manuel Valls has warned that far-right organisations are infiltrating the opposition movement, triggering unrest.

New Zealand this week voted to legalise gay marriage, making it the 13th country in the world where same-sex unions are permitted.

[Image via Agence France-Presse]