Updated 11.21am: Renewed calls for Corrections Minister Sam Lotu-Iiga to be sacked, after an investigation into Serco has been swamped with complaints.

Mr Lotu-Iinga has been unable to give specific details on extra complaints that have seen an inquiry into Serco extended.

Green MP Dave Clendon said they're aware the Minister hasn't been routinely briefed on performance audits.

He said "the fact the Minister seems not to know what has been going on there, would indicate to us that information has been kept from him."

The deadline for the investigation into the private prison operator has now been pushed back, to make sure all the issues being raised can be dealt with.

New Zealand First corrections spokesperson Mahesh Bindra said Mr Lotu-Iiga still doesn't seem to know what's happening.

"He's absolutely clueless about what Serco has been hiding from him. He's not been able to manage the whole issue very effectively."

Meanwhile the majority of voters don't want private companies such as Serco anywhere near our prisons.

A Herald-DigiPoll survey has found 57% of people always want prisons to be run by the state.

Only 38% think there's a place for well-run private prisons.

Labour's corrections spokesperson Kelvin Davis said National needs to show it's listening.

"Close to 3/5ths of the country are saying that they don't want privatisation of prisons."

"I think that's a very clear message to the government they need to kick Serco into touch."

He believes some things should always be run by the state.

"Police, armed forces and I think our prisons are also one of those instances, where the state denies people their liberty and the state should actually be responsible for looking after them."