The number of prisoners kept in segregation has more than doubled in the past six years.
The Department of Corrections says about 2300 inmates are now segregated from other prisoners.
The last census of inmates in 2003, showed 19% of prisoners were in segregation, but the department says that figure has now grown to represent 28% of the prison population.
It says most of those prisoners have requested segregation, which they can do if they express concerns for their safety.
The department says prisoners are kept in segregation until the prison manager believes their safety is no longer at risk. Inmates who are considered a threat to other inmates can also be segregated by prison staff.
Corrections service support manager Karen Urwin says prisoners in segregation have different levels of contact with other prisoners, and incidents are rare.
She says having 28% of prisoners in segregation is in line with other countries.
But Kim Workman, a former head of prisons who now leads the group Rethinking Crime and Punishment, says prisons that are well managed should not have that many inmates wanting to be segregated.
He says prisons should be teaching people how to live in a community and relate to each other.
Mr Workman says it is possible that prisoners' reasons for wanting to be segregated are not genuine, as many in segregation can still mix freely with each other.