France's National Assembly on Saturday overwhelmingly approved the key article of legislation that will allow gay couples to get married and adopt children.

Deputies voted 249-97 in favour of Article One of the draft law, which redefines marriage as being a contract between two people rather than necessarily between a man and a woman.

Although the proposed law still faces at least another week of scrutiny before a final vote scheduled for February 12, it now looks set to emerge from parliament undelayed and undiluted.

The article approved on Saturday was supported by deputies of the ruling Socialist Party, who enjoy an overall majority in the Assembly, other leftists and Greens as well as at least one member of the UMP, the main centre-right opposition force.

Massive demonstrations across the country have underlined that those who oppose gay marriage feel very strongly about the issue and President Francois Hollande has been accused of pushing the legislation through without proper consultation.

The Catholic church has been heavily involved in mobilising opposition and protests were scheduled to take place again Saturday in towns and cities across France.

A national rally in Paris last month attracted hundreds of thousands of demonstrators and was at least twice as big as a protest staged by supporters of the reform.