Actress Allison Mack has pleaded guilty in the Nxivm sex cult case, having changed the not guilty plea she entered a year ago.

German-born Mack, 36, is facing charges including sex trafficking, identity fraud and money laundering for her alleged role in running a sex slave cult in Albany, New York.

Court papers allege the purported self-help group formed a secret society of women who were branded with the initials of the founder, Keith Raniere, and forced to have sex with him.

Mack was accused of being one of the leaders and recruiters to the cult, and jury selection for the trial began on Monday.

She pleaded not guilty in April 2018, but on Monday changed her plea in Brooklyn federal court.