A Queensland University of Technology law lecturer posing online as Justin Bieber has been charged with more than 900 child sex offences.

Gordon Douglas Chalmers allegedly used Facebook and Skype to impersonate the pop star and persuade fans to send him explicit images, police say.

The 42-year-old was arrested in November last year on a string of child sex offences after a tip-off from German and US authorities led Queensland police to raid his home.

Mr Chalmers “refused” to provide police with access to his social media and messaging accounts and cloud servers, police said.

Further investigation of his computer by detectives from Argos Taskforce has led to another 931 offences.

The new charges include indecent treatment of children and making child exploitation material.

Police believe the offences began in 2007.

Detective Inspector Jon Rouse said the offences were “horrendous” and highlighted the vulnerability of children using social media.