The 22-year-old New Yorker was a headline act at the Listen Out music festival, which attracted 9000 lovers of electronic music to Centennial Park in Sydney at the weekend.

But Banks was barely 15 minutes into her 50-minute set when a can of beer was thrown at her.

Oli Wenban, from Avalon in Sydney's northern beaches, witnessed the scene.

"She was fantastic in the beginning," the 19-year-old said.

"Then someone threw a beer can about five songs in, and she said 'eff this shit' and left."

Many bought tickets to the festival specifically to see her, Mr Wenban said, and left after the rapper stormed off.

"Eventually she came back on and did [the song] '212', but her whole set was only about 15 minutes."

"It's really disappointing," he said. "She had a big vibe, she had the best outfit."

Other fans used social media to express their frustration.

I'm so disappointed with @AZEALIABANKS set at #ListenOut - To me she was just a spoilt little brat who wouldn't perform which is a shame — ☈HYS ΔUSTIN (@rhysaustin) September 28, 2013

In a series of posts on Instagram, Jordan Kretchmer dubbed her actions as "smug" and "lame".

"She played like three songs, then stormed off because someone threw something on stage (can/tennis ball).

"Finally came back on and played 212 then walked off with big smug grin. So lame!"

But other fans defended her decision to leave.

@brunobocutti people were throwing things on stage and she didn't like it! Fair enough — Sohan Judge (@SohanJudge) September 28, 2013

NSW Police said they were not aware of any complaints about an item being thrown.

"I've spoken to the police out there, they had drugs located [on 94 festivalgoers] but they didn't mention [the beer]," a police spokeswoman said.

The festival's promoter, Fuzzy Events, could not immediately be reached for comment.