A group of refugees has been attacked by a mob in Cologne, Germany, amid continuing tensions over the assaults on New Year's Eve.

Police said six people from Pakistan were set upon by a gang numbering around 20 on Sunday, leading to two of them needing hospital treatment.

In a separate incident, a Syrian man was injured after he was attacked by five people.

Investigators are looking into whether the attacks were racially motivated and if there was any link to the string of sex assaults and muggings in the city on New Year's Eve, which have largely been blamed on foreigners.

Police in the German city are now investigating 516 criminal complaints connected with the New Years' Eve attacks on women.

40% of the cases are allegations of sexual assault, while two are of rape.

It is understood officers are looking at 19 suspects as part of their investigations.

The situation has led to calls for stricter immigration rules and deportation of asylum seekers who break the law.

Those assaults have tensions over Germany's open-door policy in the refugee crisis and led to calls for tougher laws against migrants who commit crimes.

Newstalk.com's Shona Murray has just returned from Cologne. Her report contains some strong language.