Swiss voters appear to have decided by a clear margin to allow same-sex couples to marry, according to a projection after a national referendum on Sunday.

The projection by the gfs.bern polling agency for Switzerland’s public broadcasters showed the measure passing by 64 per cent to 36 per cent.

Switzerland’s parliament and the governing Federal Council supported the “Marriage for All” measure, and pre-referendum polls showed solid backing. Switzerland has authorized same-sex civil partnerships since 2007.

Supporters said passage would put same-sex partners on equal legal footing with heterosexual couples such as by allowing them to adopt children together and facilitating citizenship for same-sex spouses. It would also permit lesbian couples to utilise regulated sperm donation.