Miley Cyrus dressed as Nicki Minaj at a Halloween party with such tight security there were "confidentiality agreements".

The 19-year-old singer has been experimenting with her look of late, having shaved her hair and bleached it blonde.

She attended a party at the Beacher’s Madhouse nightspot inside Los Angeles' Roosevelt Hotel last night, in honour of Halloween. Miley went all out with her costume, donning a huge yellow, curly wig and skin-tight leopard-print catsuit as she channelled Nicki.

The star even appeared to place padding around her butt in honour of Nicki's famously large rear.

"Miley was on the stage dancing like crazy. The guest list was tight and all guests had to sign confidentiality agreements and check their cell phones," a source explained to New York Post.

Miley appeared to be very proud of her outfit, even tweeting a picture of herself pouting to Nicki herself.

A host of other stars were on hand to celebrate the spooky holiday at the event.

Miley's mom Tish went as a skeleton and her fiancé Liam Hemsworth dressed as a unicorn - perhaps following his stint as one of the mythical creatures in a recent promo Miley shot.

Zac Efron dressed as a cowboy from 2005 Brokeback Mountain. The movie followed the love affair between two men, with Zac's actor pal Ryan Rottman also going as a cowboy.

Pharrell Williams also enjoyed the bash, partying dressed as himself.