The MP who first raised questions about how Serco was running Mt Eden Prison has fresh allegations about another prison run by the private operator.
Labour's Kelvin Davis said the wife of an inmate at the Auckland South Corrections Facility at Wiri had told him serious beatings at the men's prison were going unreported, and that prisoners were being locked-down almost all day long.
The prison is the country's largest public-private partnership and opened in May.
But Mr Davis said an inmate had complained it was well on its way to becoming like Mt Eden Prison - which, until recently, was also run by Serco.
He said the new allegations showed privatising prisons was a complete failure.
The complaints are detailed in an email from the inmate's wife to the MP:
"He's very concerned - he's said there's already serious beatings happening - and he doesn't believe they're all being reported.
"There are also units being locked down for 23 hours a day, there is no staff on the floor so you can never find anyone and no-one is ever observing what the inmates are doing.
"No-one is searched going in and out of visits - just what he describes as a 'half-arsed' pat-down," said Mr Davis, reading the email from the woman - who did not want to be named.
The Te Tai Tokerau MP was speaking at a discussion last night organised by the JustSpeak group about private prisons.
He later told Radio New Zealand he got the email with the allegations only that day.
"We've seen it in Mt Eden and now we're seeing it in Auckland South [Prison].
"I visited Auckland South with our select committee a few weeks back and everything seemed fine on the surface but we don't know what happened once the gates were closed behind us.
"From the look of this email from this woman it looks like it's no different to what has been going on in Mt Eden," Mr Davis said.
Allegations yet to be raised with Serco
Serco director of operations Scott McNairn said in a statement to Radio New Zealand that the claims had not been raised with the prison operator.
"We encourage anyone who has a specific allegation to notify us, or the Department of Corrections, so that it can be properly investigated."
"The safety and security of prisoners, staff and visitors in Auckland South Corrections Facility, as well as the wider community, is their priority, and ASCF is staffed accordingly," it said.
"Assaults in prison are illegal, unacceptable and we will not tolerate them. Any perpetrators should expect to face criminal charges as well as prison disciplinary processes. Incidents are notified to the Department of Corrections, investigated and reported to the police."
The statement said the prison had robust measures to detect and prevent the smuggling of contraband, including searching of every person, prisoner, visitor or staff member who entered.
The Auckland South Corrections Facility is a $300 million prison with space for 960 inmates.
Its standard cells have televisions which double as computers, and telephones for prisoners to ring pre-approved numbers.
Mr Davis said it didn't matter what technology there was if prison systems were not up to scratch.
"I do recall getting an email from someone's family from Auckland South with similar concerns... maybe it's the start of something," he said.
The Department of Corrections was put back in charge of Mt Eden after a string of allegations of mismanagement levelled against Serco.
An investigation into organised prisoner fighting at Mt Eden is due at the end of this month after being extended by two months because of the high number of complaints from prisoners and their families.
Corrections Minister Same Lotu-Iiga has previously said Serco's operation at Auckland South Corrections Facility would also be looked into, although at the time he said he held no concerns.