There's only 300 beds left in New Zealand prisons, but do we need a 3000-bed facility?

New Zealand is running out of space in our jails, with too many inmates and not enough room.

In 2017, the number of Kiwi inmates hit 10,000 for the first time and it's now close to 11,000 across the country's 18 prisons.

New Zealand now has 300 beds left and it's not because of population growth.

Since 1986, the number of those behind bars has quadrupled, far outpacing the population.

In the last five years alone, the number of prisoners has surged 24 percent.

The National Government was planning to build a 3000-bed prison in Waikeria, rural Waikato, to cope, but that's now in limbo.

Corrections Minister Kelvin Davis has suggested the super jail could be scrapped, but where would that leave the prisoners?

Criminology professor Liam Martin spoke to Three's The Project about whether the prison needs to be built.

He's not in favour, saying some changes to how long we hold prisoners could help reduce the need to a mega prison.

"I think we should be targeting bail laws," he said.

"A lot of our recent increases in prison numbers have come through the Bail Amendment Act in 2013, which really dramatically increased the number of people who are being held in prison while they wait for their trial."

"Another option is parole. In recent history, we've dramatically increased the proportion of sentences being served, so that people are being held in prison for much longer."

Watch the video for the full The Project interview.