Police in Germany are hunting for a man sporting a Hitler moustache who attacked two Afghan refugees with a Nazi helmet before fleeing.

The man verbally abused the pair before attacking them while they were sledding in the mountains of Altenberg, near the German border with the Czech Republic.

After he struck them with the helmet, passersby intervened and he then performed a Hitler salute, police say.

The pair of refugees were sledding in Altenberg (pictured), Germany, when they were attacked by the man sporting a Hitler moustache

One of the victims, who were aged 21 and 26, needed to be hospitalised after the attack, Bild reported.

The paper said the attacker was wearing light blue jeans and a khaki jacket, while he was aged between 25 and 30 and was bald.

The incident arises amid high tensions across Germany following the New Year sex attacks in Cologne.

The scale and nature of the crimes in Cologne, coupled with police descriptions of the perpetrators as being part of a large crowd of drunken men of 'Arab or North African' origin, has fanned the debate about Germany's approach to migration.

Almost three weeks after the incident, 838 people have filed criminal complaints, including 497 women alleging sexual assault.

Yesterday a 26-year-old Algerian man has become the first person arrested in connection with a string of sexual assaults.

Prosecutors said the unidentified asylum-seeker was arrested at a refugee home in the nearby town of Kerpen over the weekend.

He is accused of groping a woman and robbing her cellphone, prosecutor's office spokesman Ulrich Bremer told The Associated Press.

Two other Algerian asylum-seekers, aged 22 and 24, were also arrested in Kerpen and the western city of Aachen, respectively, over the weekend, both for robbery, Bremer said.

The number of people accused of committing crimes in Cologne at New Year's now stands at 21, of whom eight are in detention, he said.

While the incidents were seized on by those in Germany who had already argued for stricter immigration rules, left-wing parties have also voiced concern.