The number of prisoners in New Zealand has reached a new high.

Corrections Minister Judith Collins said today there were 8520 prisoners in prisons or police stations nationwide.

The number has been steadily growing - on September 21 it was 8509, 16 higher than the previous peak of 8493 on September 7.

In 1996/97 the average prison population was about 5000.

The rising prison population trend could not continue, Ms Collins said.

The social and economic costs were "immense".

The number showed the need for education, training and rehabilitation in prisons, she said.

"While some (prisoners) are plain bad, for others reoffending is the result of them being poorly equipped to lead a law-abiding and productive life."

The Prisoner Skills and Employment Strategy will see an extra 1000 prisoners get skills and work and the Government had also committed to three additional drug treatment units, Ms Collins said.

"If we are to bring prisoner numbers down we must look very seriously at addressing drug and alcohol addictions that lead to crime and ensure prisoners have good work skills and can find a job.

"When we release people from prison we don't want to see them back," she said.

The Government has previously announced it would build a container cell block at Rimutaka prison and would use double bunking to make space.