The 'Hold it Against Me' hitmaker caused a furore when she turned up at the West Hollywood bash to join the rapper onstage at The Factory nightclub.
A witness told E! Online: "[It] was complete pandemonium. Six people were carried out after hyperventilating. They literally fainted when Britney walked onto the stage where Nicki was hanging.
"People were crowd surfing to get to the stage. Screams were so loud for Nicki and Brit you couldn't hear the music. Bouncers couldn't hold the crowd back."
The 29-year-old star clearly enjoyed her impromptu performance and wrote about it afterwards on micro-blogging website twitter.
She wrote: "Hanging with my girl Nicki Minaj at her after party at The Factory. Love you girl."
Nicki recently announced that she will be joining Britney on her Femme Fatale tour as the opening act.
Although she has decided against collaborating with other artists for the near future she said she was willing to make an exception for pop princess.
She said: said: "I'm done with collabs. No more collabs for the next two years. Although - Britney's a snatch like me and she's cute. Yes. We might do something."
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