Slim Jxmmi also posted a live video on Instagram showing a bandaged hand, along with footage of the Sky Tower.
Detective Senior Sergeant Kathryn Bostock said two men are assisting police with inquiries, however the investigation is ongoing.
"This is an area with a lot of people out and about and we'd like to hear from anyone who saw what happened or anyone who filmed it on their phone. We urge you to contact Auckland Police," she said.
No charges have been laid at this stage.
Jxmmi and his brother Swae Lee, who have released three albums and are best known for their single Black Beatles are performing at the Logan Campbell Centre in Epsom on tonight.
A witness told the Herald he heard a scuffle and a bottle shattering at about 4pm. When he looked over he saw seven men fighting and the broken bottle being used as a weapon.
Another witness said the American group were walking down the street when someone called out to them, sparking a verbal confrontation. The American group appeared to be walking away when they were attacked by a member of the other group, the witness said.
One man who contacted the Herald saying he was involved said he challenged the Americans because they were filming a friend of his - a homeless man who had been drinking.
He thought it was inappropriate and in turn decided to film the group himself but they took offence to being filmed and confronted him.
He said words were exchanged between the two parties before a fight ensued.
The Herald is trying to reach Rae Sremmurd for comment.
