A man and woman were taken to hospital with facial injuries after they were assaulted by four men who jumped out of a black Audi.
The victims were among a group of around nine people in their twenties walking in Tanfield Lane, Middleton in the early hours of Saturday morning.
At around 12.15am the black Audi car pulled up alongside the group and some of the women were verbally abused.
Four men got out of the car and assaulted four of the group.
The pair with facial injuries have since been discharged from hospital. Two men also sustained minor injuries, which did not require hospital treatment.
All the victims who were injured are 21 years old.
The offenders are four white men, all aged in their mid to late twenties.
Investigating officer Detective Constable Mandy Banfield said: “We are in the early stages of this investigation and we are establishing what has happened.
“We would like anyone with information to come forward, we believe a car which was not connected to this incident did drive past during the assault and we would like to speak to this person.
“It happened in the early hours and it is likely other vehicles passed this incident at the time, so if you saw anything we would encourage you to get in touch, even if you think your information is not significant.
“If anyone has CCTV footage or dash-cam footage from the area at this time, we would also like to review this.
“Enquiries continue and at this time it is being treated as an isolated incident.”
Please contact Thames Valley Police on 101 quoting reference 43190204586 or make a report online.
If you do not wish to speak directly with police, you can call the independent charity Crimestoppers 100% anonymously on 0800 555 111.