Berlin  - Voter support for German Chancellor Angela Markel's Social Democratic (SPD) coalition partner has slumped to a new low, according to an opinion poll released on Wednesday.

The survey, taken less than three months before the country votes in a general election, showed the left-of-centre SPD down 1 per cent from a week ago to 21 per cent, its lowest ranking this year.

Merkel's conservative Christian Democrats (CDU) were steady at 36 per cent, according to the poll conducted by the Forsa research institute for the magazine Stern and the RTL television network.

The business-oriented Free Democrats (FDP) polled 15 per cent, while the environmentalist Greens were on 12 per cent and the radical Left party on 11 per cent.

Merkel told a party congress on Monday she hoped to jettison Foreign Minister Frank Walter Steinmeier's SPD after the September 27 election and form a centre-right coalition with the FDP.

The two parties would have an absolute majority of 51 per cent in the lower house, the Forsa poll showed.(dpa)