Tens of thousands of demonstrators rallied in Germany on Saturday, urging citizens to vote against the far right in this weekend's European Union elections.

With placards reading "Stop hatred" and "Down with racism", around 30,000 people joined a demonstration in central Berlin, according to Campact, one of the civil groups organising the rally.

Polls indicate the anti-immigration AfD party could win up to 15 percent of the vote in Germany on Sunday -- potentially its best ever performance -- despite a string of scandals.

That would place it joint-second with Chancellor Olaf Scholz's Social Democratic Party and behind the centre-right Christian Democrats.

Some demonstrators in Berlin held up letters spelling out "Go vote" along with yellow stars like those of the EU flag.

"There is no better way to defend democracy than to go and vote tomorrow," activist Tareq Alaows of the refugee rights group ProAsyl told the crowd.

Thousands of people joined similar rallies in Stuttgart, Leipzig, Dresden, Munich and Frankfurt.

The AfD was expelled from a far-right group within the European Parliament after its top candidate Maximilian Krah made comments minimising the crimes of the Nazis' SS guards.

Among other scandals, Krah is also being investigated over his relations with China after one of his aides was arrested on suspicion of spying for Beijing.

At the start of the year, media reported that members of the party attended discussions of plans for mass expulsions of foreigners from Germany.

The report sparked weeks of mass protests.

At his final campaign rally for the election in the western city of Duisburg, Scholz urged people to vote on Sunday "to defend democracy and the rule of law".