Officers were called to reports of a girl being sexually assaulted by four men at Fishponds Park just before 7.15am yesterday (August 21).
A crime scene has been established at the park as forensic searches continue and enquiries are ongoing.
The teenage girl is being supported by specialist officers.
Four men have been arrested on suspicion of sexual offences including rape and remain in custody.
A 24-year-old man has been arrested on suspicion of sexual assault and administering a substance with intent to commit a sexual offence.
A 36-year-old man has been arrested on suspicion of rape, sexual assault and administering a substance with intent to commit a sexual offence.
A 35-year-old man has been arrested on suspicion of rape, sexual assault and administering a substance with intent to commit a sexual offence.
A 41-year-old man has been arrested on suspicion of rape.
A spokesperson for Metropolitan Police said: “We understand this news is concerning for the community and we will be increasing patrols in the area.
“If you have any information, please contact 101 quoting CAD 1207/21AUG.”
