After an attack in northern Germany that injured a Ghanaian girl and her father, the police received multiple tips, including information about possible suspects, a police spokesman told dpa on Sunday.
The investigation is extensive and will take some time, he added.
According to initial police findings, an 8-year-old Ghanaian girl and her 10-year-old sister were attacked by a group of around 20 teenagers and young adults. The 8-year-old and her father, who intervened, were taken to hospital with injuries described as mild.
The alleged racist attack has sparked outrage from politicians and led to a public outcry.
The attack took place on Friday evening in the town of Grevesmühlen in the north-eastern state of Mecklenburg-Vorpommern.
The attackers are said to have kicked the younger girl in the face. When the children's parents intervened, a fight broke out.
Reports indicate that the attackers shouted racist slogans during the town festival, and up to eight individuals from the group are now under investigation for several crimes including grievous bodily harm and incitement of hatred.
Other incidents with suspected racist motives occurred in the region over the weekend, including a group performing Nazi salutes in the state capital Schwerin and a violent altercation in the small town Penkun, which is located near the Polish border, involving racist chants.
These incidents have heightened concerns about rising racism and violence in the area.
The mayor of Grevesmühlen, Lars Prahler, said he was shocked by the violence.
"This racially motivated offence simply leaves me stunned. It shows bottomless hatred and uninhibited inhumanity and cannot be excused." The fact that they were teenagers is also no excuse, he added.