Swiss voters appear set to back a proposal to open civil marriage and the right to adopt children to same-sex couples, according to early indications published by Swiss broadcaster SRG.
Projections show 64 per cent of voters voted in favour of same-sex marriage in a nationwide referendum conducted under Switzerland's system of direct democracy on Sunday.
A final result is expected later in the day.
"We are very happy and relieved," said Antonia Hauswirth of the national committee Marriage for All, adding that supporters would celebrate in Switzerland's capital Bern on Sunday.
Amnesty International said in a statement that opening civil marriage to same-sex couples was a "milestone for equality".
However, Monika Rueegger of Switzerland's right-wing Swiss People's Party (SVP) and member of the referendum committee No to Marriage for All said she was disappointed.
"This was not about love and feelings, it was about children's welfare. Children and fathers are the losers here," she told Reuters.
The amended law will make it possible for same-sex couples to get married, and to adopt children unrelated to them.
Married lesbian couples would also be allowed to have children through sperm donation, currently legal only for married heterosexual couples.
It will also make it easier for foreign spouses of a Swiss individual to get citizenship.
In a separate referendum, 66 per cent of Swiss voters looked set to reject a proposal to introduce a capital gains tax.