BERLIN: Chancellor Angela Merkel has opened the door to a law allowing gay marriage in Germany, softening her stance before a September 24 election on an issue potential coalition partners have made a condition for sharing power.

Merkel said at an event hosted by women's magazine "Brigitte" on Monday evening she had taken note of other German parties favouring same-sex marriage.

"I would like to lead the discussion more into a situation where it is a question of conscience rather than something I push through with a majority vote," she said, when asked about her position.

The Social Democrats (SPD), junior partners in Merkel's right-left "grand coalition", the pro-business Free Democrats (FDP) and the Greens - all potential coalition partners after the election - have made gay marriage a condition for a tie-up.

Responding to the announcement, SPD leader Martin Schulz said on Tuesday his party would even push for a vote in parliament this week.

With broad support among Germans for gay marriage, the law would likely get easy approval in the lower house if conservatives could vote according to their conscience and not face a party whip.

Polls put Merkel's conservatives 10-15 points ahead of the SPD, but short of a parliamentary majority.

Fearful of antagonising some in her traditionally Catholic conservative parliamentary bloc who oppose it, Merkel has previously argued against same-sex marriage.

Same-sex civil partnerships have been allowed in Germany since 2001 but marriage is a step up from that.

The LSVD association representing homosexuals welcomed what they said was a belated shift, saying it was a face-saving measure to exit a dead end. They called for a vote in the Bundestag lower house before the election.

"After 15 years of an ideological blockade .. social pressure and the commitments of other parties have made an impact," said LSVD spokesman Axel Hochrein.

"Equal rights for all people is part of our constitution," he added.