Police were called to a warehouse in Aztec West at about 22:45 GMT following complaints about noise.
Between 400 to 500 are estimated to have been present, police said, and the majority of the crowd had dispersed by 03:30 on Thursday.
Just one person was arrested on suspicion of offences including drug possession and supply, driving under the influence of drugs and remains in custody, while two vehicles containing sound equipment were seized.
An estimated 400 people were found at an industrial site in St Phillips after police were called at 23:15, and Feeder Road was closed to prevent more people attending.
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