The deputy leader of the German far-right AfD party Beatrix von Storch is under police investigation following social media posts she made on New Year's Eve.

Von Storch hit the roof when Cologne police tweeted a Happy New Year greeting in Arabic.

"What the hell is going on in this country?" howled Von Storch on Twitter. "Why did an official police site from North Rhine-Westphalia tweet in Arabic? Do you think that you are going to appease the barbaric, muslim, gang-raping hordes of men?"

Von Storch's reference to the mass sexual assaults of New Year 2015 in Cologne may mean she is the first person to be found guilty under Germany's controversial new NetzDG law, which from January 1 cracks down on social media hate speech. The comments led to brief Facebook and Twitter bans.

Von Storch's boss, AfD leader Alice Weidel has been scathing about social media censorship, and backed Von Storch with a post of her own.

"The year begins with the censorship law and the submission of our authorities to the imported, marauding, graying, flogging, knife-stabbing migrant mobs, which we should get used to," she posted on her facebook page.

Once her 12-hour ban was lifted, Von Storch went back on the offensive.

"Facebook has also censored me. That is the end of the constitutional state," she said.