"One of the prisoners passed out due to becoming overwhelmed with heat and dehydration and was saturated with sweat."
The father said the prisoners tried to notify the driver and guards by yelling and kicking the sides of their "little cages" but didn't get a response.
"It wasn't until arrival that the driver and guard realised they had failed to turn on or check the ventilation was turned on and operational," he said.
"This is not for comfort, this is for survival and we demand more for animals and infants ... I know they are prisoners ... but this amounts to gross negligence and basic human rights in a first-world country not being adhered to I would think."
Chief custodial officer Neil Beales said the very high temperatures this week had been uncomfortable for prisoners, staff and people in the community.
"During a scheduled rest and hydration stop at Manawatu Prison at around 5pm, staff became aware that a prisoner being transported was unwell," he said.
"All prisons have a health centre on site and medical staff were advised, and the prisoner was assessed and treated. Other prisoners continued on to Rimutaka Prison without incident."
Beales said the vehicle was checked by an engineer who concluded the weather conditions affected the motor running the air conditioning unit. He said the vehicle would not be used until the issue had been fixed.
"Prisoners inside the vehicle are monitored on camera by staff," he added.
"Any concerns raised by prisoners during the journey will be captured by a review that we are undertaking of the incident."