The AfD has experienced a late increase in support which has put the party in third place after Mrs Merkel’s Christian Democrats and her coalition allies, the SPD.
With the latest gains, the AfD is almost certain to enter Germany’s national parliament for the first time next Sunday, making the nationalist party the coalition’s main opposition.
The AfD’s surge has come following leader Alexander Gauland’s calls for Germans to feel proud of Nazi military achievements.
The 76-year-old is also under police investigation after calling for Germany’s national integration commissioner, Aydan Özoguz, who is German-born and of Turkish heritage, to be “disposed of in Antolia”.
German foreign minister Sigmar Gabriel said this week: “We will have real Nazis in the Reichstag for the first time since the end of the Second World War.”
However, Mr Gauland dismissed the warnings, telling his supporters: “Don’t believe anything the other parties and politicians say about me.
“Remember, when you are in the voting booth no one is looking over your shoulder, no one can see where you put your cross.”
He added: “I don’t believe Sigmar Gabriel is stupid enough to really believe we are Nazis.”
The party’s hopes were not being taken seriously due to ongoing infighting and a vote to marginalise Frauke Petry, its official leader who was seen as its strongest asset.
The campaign was handed over to Mr Gauland and Alice Weidel, from outside the party, which many thought would be the end of the AfD.
However, Mr Gauland has been able to play on the party’s core issue of immigration to gain a late surge in the polls.
Talking in his constituency of Frankfurt an der Oder, where unemployment is high, he told crowds: “We don’t want to be the world’s doormat.
“We want our country back.”
He told them there will be 240million more Muslims in Europe by 2050 and praised Donald Trump for “actually doing what he promised”.
Gero Neugebauer, a political scientist at Berlin’s Free University, said: “If you look at the polls, 40 to 46 per cent say they haven’t made up their minds, and we have no idea how the pollsters are factoring that into their calculations.
“On top of that you have the question of shy AfD voters, people who might not want to say they’re going to vote for the party in public because of the negative publicity, but who could choose it in the privacy of the voting booth.”