The Alternative for Germany party is polling above 20 percent in the northeastern state of Mecklenburg-Western Pomerania, where Chancellor Angela Merkel has her electoral seat.
Support for the AfD in the state is at a similar level to Merkel'sconservative CDU and just behind the centre-left Social Democrats.
"The voters aren't realising they are voting for a party that doesn't want to distance itself from the far-right spectrum," president of the Central Council of Jews in Germany Josef Schuster told AFP Friday.
The AfD, which gained support when Germany took in a huge influx of refugees, "offers just slogans, no solutions", said Schuster.
Merkel said in an RTL television interview she wanted to encourage people to vote "and to vote for parties that offer solutions to problems," adding that the AfD was not one of them.
The AFD, founded as an anti-EU party, has shifted to an anti-Islam and anti-migrant platform, protesting the arrival in Germany of a million asylum seekers in 2015.
Since 1945, no far-right party has managed to establish itself permanentlyin the German political landscape.
But recent polls have given the AfD 10 to 15 percent support ahead of national elections next year.
Schuster said that if citizens worried about the huge refugee influx and about recent jihadist attacks, then "to an extent this is understandable, but no reason to vote for the AfD".