Germany's Social Democrats are ignoring slumping polls and a disastrous showing in recent European elections, insisting at a party conference that the country's parliamentary election is still "open."

Social Democrat chancellor candidate, Foreign Minister Frank-Walter Steinmeier, called on about 500 delegates gathered in Berlin on Sunday to stage a "furious campaign" before September balloting.

"Everything is open. We will keep it open and win in the end," Steinmeier said to the group, which will set the party's platform for the election.

The Social Democrats face a serious battle. A poll Friday showed the gap in support between the Social Democrats and their main rival, Chancellor Angela Merkel's Christian Democrats, grew again, after the party drew a record-low 20.8 percent of the vote in European parliamentary elections a week ago.

Just 25 percent of Germans polled for broadcaster ZDF said they would vote for the Social Democrats if the election was held this Sunday, a 3 percentage point drop from the previous poll in May.

Steinmeier criticized Merkel for failing to act with swift decisiveness when tackling key issues.

"Germany can no longer stand that," Steinmeier said. "It's about leadership, it's about clarity and direction."

Yet the Social Democrats will have their work cut out for them in trying to shake Germans' faith in Merkel, whose party gained a percentage point to 37 percent support, the poll showed.

The Free Democrats, a pro-business party and Merkel's preferred coalition partner, gained 1 percentage point for 13 percent support — just enough to give them and the Christian Democrats a majority.

The poll conducted for ZDF by the Mannheim-based Elections Research Group questioned 1,343 randomly selected eligible voters between June 8-10.