The prison population has surged by hundreds since Christmas, just as an entire high-security complex was destroyed in mayhem at Waikeria.
"If the muster continues to increase, we're going to have difficulty finding the right beds," Corrections Association president Alan Whitley said today.
The Department of Corrections said it was normal for the muster to rise at this time of year, for reasons including courts closing during summer holidays.
But from December 29 to January 3, Waikeria experienced the longest, most damaging New Zealand prison riot in decades.
A department spokesman said the prison population on January 12 was 8,739.
That was 351 more than on Christmas Eve.
The release of some eligible prisoners before the December 15 to January 5 holiday period also affected muster numbers.
The Parole Act gives Corrections discretion to free some eligible inmates in early December if prisoner statutory release dates fall within the holiday period.
A Waikeria complex with capacity for 251 prisoners was wrecked in the riot.
Police are yet to charge anyone in relation to the fires and disorder at the high-security complex.
Whitley said it would not be surprising if a complex investigation occurred.
"It's clearly going to take a while to get the charges."
He was confident charges would eventually be laid.
"No-one's going to let it slip under the radar."
The spokesperson said on Wednesday that there was no issue regarding lack of capacity in the prison network following the Waikeria Prison riot.
"The prison population peaked at 10,820 in March 2018. Since March 2018 the prison population has dropped significantly and today's figure is 8,738.
"Currently there are over 1000 additional beds available in the prison network, without the beds currently being added through the modular unit project.
"The decrease in prison numbers prior to Christmas and the subsequent increase over the Christmas period is something we face every year and is not new to us. Our staff understand this and are experienced and well prepared to manage any fluctuations in the population."
Prison reformist Sir Tā Kim Workman today said an independent review of Waikeria and broader prison estate problems was needed.
"It would be great to see an independent group do the work, probably a well-known QC, probably someone who's prominent in Te Ao Māori" (the Māori World).
He said the review team should also include someone familiar with the criminal justice system.
Workman said a thoughtful approach would be needed.
"The whole thing is in danger of being politicised to the point where people will feel unable to move forward."
He said New Zealand jails had long-standing problems with racism, high levels of Māori incarceration, and young inmates being pressured to join gangs.
"It requires courage in terms of political leadership, that courage to stand up like Andrew Little did at the beginning of his term as Minister of Justice and say: The system is stuffed, racism is inherent in the system."
Minister of Corrections Kelvin Davis described the Waikeria chaos as an inexcusable riot involving mostly Mongol and Comanchero gang members.
Last Sunday, he said Corrections would review how the situation unfolded and escalated.
NOT SO FAST
Meanwhile, some delayed modular units in the "rapid build" fiasco are nearing completion.
One modular unit at Canterbury's Rolleston Prison should be ready by February 1, the Department of Corrections said.
A second Rolleston unit and another at Tongariro Prison near Turangi were expected to be finished by the end of February.
Chinese company CIMC made the modules, which Australian company Decmil's New Zealand subsidiary were supposed to deliver.
The project ballooned from a proposal for three 126-bed units at Rolleston and Tongariro four years ago into a sprawling, nationwide 976-bed project.
And the $400 million deal descended into acrimony and finger-pointing after delays and allegations some units were leaky or faulty.
Last year, Corrections terminated its contract with Decmil NZ for the modular prison places.
Decmil NZ went into liquidation and both sides took their dispute to court.
A Christchurch Women's Prison unit was expected to be completed in mid-2021.
Units at Christchurch Men's Prison and Rimutaka Prison in Upper Hutt were expected to be ready by the end of 2021, Corrections added.
Whitley said it was mind-blowing to think a 126-bed, low-security unit could take more than three years to build.
"The rapid builds have been anything but rapid."