A double-digit score for the anti-immigrant Alternative for Germany (AfD) party in a Berlin city vote would be seen around the world as the rebirth of the Nazis, the mayor of the German capital has warned.
The right-wing AfD has gained support as voters become increasingly uneasy with Chancellor Angela Merkel's open-door refugee policy, which saw about one million migrants arrive in Germany last year.
A poll published on Thursday showed the party was expected to get 14 per cent of the vote in Berlin - a historically left-wing stronghold.
"It would be seen around the world as a sign of the return of the right-wing and the Nazis in Germany," Berlin Mayor Michael Mueller, a Social Democrat (SPD), wrote on Facebook on Thursday.
"Berlin is not any old city - Berlin is the city that transformed itself from the capital of Hitler's Nazi Germany into a beacon of freedom, tolerance, diversity and social cohesion."
The centre-left SDP runs the city of Berlin in coalition with Merkel's Christian Democrats (CDU).
However the AfD party, led by young chemist Frauke Petry, has been making huge gains in recent months, winning nearly 21 per cent of the vote in an election two weeks ago. It is now represented in nine of Germany's 16 state assemblies.
The warning comes as EU leaders meet in Bratislavia for their first summit without the UK taking part.
European Council President Donald Tusk said ahead of the summit the countries need to have a "sober and brutally honest assessment" of the situation.
"I am absolutely sure that we have to assure, here in Bratislava and also after our meeting, our citizens that we have learned the lessons from Brexit, and that we are able to bring back stability and a sense of security and effective protection.
"It is true that Europe has recently been shaken by all kinds of crises but as the same time it is my feeling that the best motto for the Bratislava meeting is that we must not let these crises go to waste."