The Department of Corrections is paying for guards from three more prisons to stay in hotels as a stopgap to cope with growing inmate numbers.
This comes after it was revealed in December that Corrections paid about $2 million over 18 months for hotel rooms for guards at Mount Eden prison.
But guards are also being seconded from other parts of the country to Northland, Rimutaka and Waikeria prisons.
Corrections said it had negotiated cut-rate prices with the hotels.
"Prices are negotiated with these providers and are generally significantly discounted from the providers' normal rates," deputy National Commissioner Rachel Leota said in a statement.
Corrections said it had to ensure it has enough beds across the prison network and enough staff to safely manage prisoners.
The department would not reveal what it was spending or how many rooms it needed, saying it was just "a small number of staff".
It is understood about 30 guards across the Northland, Rimutaka and Waikeria prisons are housed in hotels.
At Mt Eden, up to 40 guards a night have been staying in hotels, but that is dropping as Corrections takes over the running of the prison entirely from private operator Serco at the end of this month.
A small number of seconded staff who stay in hotels will be kept on at Mt Eden to help the new guards get up to speed.
The extra cost of using hotels will continue until 1800 permanent beds are built as part of the billion-dollar-plus prison expansion programme.
Corrections said in December it was trying to recruit 800 extra staff by this September, when just a short time before it had said it needed 600.
This followed it laying off nearly 200 staff in 2015.