The Swiss public has voted overwhelmingly in support of same-sex marriage in a national referendum, but the Swiss Evangelical Alliance said after the poll that "the freedom of churches must be protected" and that the vote went too far.

Nearly two thirds of Swiss (64.1%) backed the "Marriage for All" proposal in the nationwide referendum on Sept 26.

Commenting on the result, the Swiss Evangelical Alliance said the "Marriage for All" referendum went "too far" and "places too little weight on the rights of children."

"The wishes of adults have triumphed over the rights of children," it said.

Gay couples had been able to enter into civil partnerships since 2007.

Although the proposals have now passed the referendum, it could be several months before the change comes into effect.

Swiss Justice Minister Karin Keller-Sutter told a media briefing that the new rules would likely come into force on July 1 next year, Reuters news agency reported.

The evangelical alliance expressed further concerns about the development of further legislation in the future to permit egg donation and surrogacy.

"An extremely dubious instrumentalization of the human body was not given enough consideration," it said.

The Swiss EA pledged to stand up for the religious freedom of pastors and churches following the vote.

It said churches must be free to wed only heterosexual couples.

"The Swiss Evangelical Alliance will continue to campaign for freedom of religion and freedom of conscience with regard to church weddings," it said.

The SEA RES together represents some 250,000 German and French-speaking Christians of evangelical conviction, including just over 40,000 for French-speaking Switzerland.

Internationally, SEA RES is affiliated with the World Evangelical Alliance.

Switzerland was one of the last four countries in Western Europe to deny homosexual couples the right to marry, Swissinfto reported.