Sunday's election win for the AfD in the Saxony-Anhalt election, where they earned 44 per cent of the vote, brought Germany's far right closer than ever to gaining power since World War II.
In Dusseldorf, around 20,000 people took part in a protest march "against the AfD and right-wing hatred," according to police and organisers, while organisers said a further 25,000 marched in Hamburg.
In Berlin, several marches against the normalisation of far-right politics converged on the city's town hall.
Police put the number of participants at 18,000, while organisers said 32,000 took part.
In several cities, rallies were also held as part of the nationwide initiative demanding that Germany's Constitutional Court review parties suspected of being or confirmed to be far-right extremist by Germany's domestic intelligence agency.
The AfD is monitored nationwide by the domestic intelligence agency as a suspected extremist organisation.
Several of its state branches, including those in Thuringia and Saxony-Anhalt, are classified as far-right extremist.
Following the AfD's election success in Saxony-Anhalt, North Rhine-Westphalia state premier Hendrik Wüst proposed setting up a joint federal-state working group to examine whether a ban on the party could be pursued.
The proposal has won support from some politicians but has also met with scepticism.
Only the Bundestag, the lower house of parliament, the Bundesrat, the upper house, or the federal government can apply to the Federal Constitutional Court for a party to be banned.
Any ban would be decided by this court.
