The Christmas Island immigration detention centre is in lockdown after a decision by the Australian Border Force to start housing sex offenders there sparked a string of brutal assaults.

Fairfax Media understands at least three men with serious sex crime convictions have been bashed by other inmates since being released into the general detainee population, rather than being housed in a segregation unit.

Christmas Island detention centre, formerly used to house asylum seekers, has been converted into a detention centre for about 200 foreign nationals whose visas have been revoked on character grounds under section 501 of the Migration Act. Credit:Getty Images

Christmas Island, which was formerly used to house asylum seekers, has been converted into a detention centre for about 200 foreign nationals whose visas have been revoked on character grounds under section 501 of the Migration Act.

The trouble started shortly after the sex offenders were transferred to the island late last week on a charter flight from Perth. The foreign nationals, who have had their Australian visas revoked over sex crime convictions, had previously been in protective custody units at mainland detention centres.