Gender-neutral marriage legislation has been adopted in Sweden, passed by a broad majority in parliament after a six-hour debate.

"The decision means that gender no longer has an impact on the ability to marry," the government said on its website.

The new legislation will come into effect on Friday 1 May, replacing law approved in 1995 which allows same-sex couples to form a union in Sweden via a registered partnership.

The Scandinavian country is known for its gay-friendly laws and culture. Homosexuality was legalised in 1944, and the Swedish Constitution bans discrimination on grounds of sexual orientation.

Sweden now joins the Netherlands, Belgium, Spain, Canada, South Africa, Norway, and parts of the United States in allowing its gay and lesbian citizens full marriage equality.