The reform would grant full marital rights - including the possibility to jointly adopt children - to gay and lesbian couples, who in Germany are now only able to enter civil union

Germany's parliament is set to vote on a bill to legalise same-sex marriage on Friday after the lower house legislative committee put it on the agenda, its chairwoman said.

"The path to equality is open," said the Chairwoman, Renate Kuenast of the left-leaning ecologist Greens opposition party, in a tweet on Wednesday.

The bill is widely expected to pass as it is backed by most parties and Chancellor Angela Merkel has told lawmakers of her centre-right party that they can vote according to their conscience.

The reform would grant full marital rights - including the possibility to jointly adopt children - to gay and lesbian couples, who in Germany are now only able to enter civil unions.

The bill was hastily put on the parliamentary agenda on the last day before the summer break by the centre-left Social Democrats, Greens and far-left Linke party.

They acted after Merkel had on Monday night dropped her long-time opposition to the reform, sparking widespread calls for a speedy vote.

Merkel had long voiced personal reservations about gay marriage with adoption rights, citing concern about "the well-being of the children".

Last Sunday, her junior coalition partners and election rivals, the Social Democrats (SPD), upped the ante by declaring they would insist on same-sex marriage in any future alliance.

All other political parties hold the same view, leaving Merkel's party opposed along with the hard-right Alternative for Germany (AfD).

Merkel signalled her shifting position Monday in an on-stage interview with the editor of women's magazine Brigitte.

She said her thinking had changed after a "memorable experience" when she recently met a lesbian couple who lovingly care for eight foster children in her Baltic coast constituency.