A gang of six males sexually assaulted one woman and punched another in the face in a brutal overnight attack in central Melbourne.
Police say the same group may be responsible for a string of robberies across the city on Friday night and Saturday morning.
Sergeant Megan Stefanec said the two women had been walking down Queen Street just before 4am on Saturday.
"Two women were assaulted and had a speaker and tobacco stolen by a group of six male offenders," she said.
"One woman was sexually assaulted and the other woman was punched to the face before the offenders fled.
"One of the offenders is described as being African in appearance, aged in his late teens and wearing a white T-shirt with Balenciaga printed on the front."
Earlier, two people were taken to hospital after being bashed in the CBD.
Sergeant Stefanec said the pair was in Banana Alley about 12.15am when they were confronted by a gang who stole their tobacco and attempted to grab a mobile phone.
"The offenders fled and were chased by the victims before the offenders confronted the victims and assaulted them," she said.
"The victims received non-life-threatening injuries and were conveyed to hospital."
Two others were also robbed outside a Southbank restaurant about 7am, with one of the victims injured after being headbutted.
They had been on the corner of Clarendon Street and City Road when they were attacked and had their mobile phones stolen by two males.
On Friday, a group of five males tried but failed to steal a man's phone and wallet in Swanston Street about 8.45pm.
Police are investigating whether the four incidents are linked.
Two men have been arrested over the robberies and police are searching for others believed to have been involved.
Anyone with information should contact Crime Stoppers on 1800 333 000.