Corrections will get an extra $355 million over four years to help cope with a growing prison population, reduce re-offending - and deal with the threat posed by deportees sent from Australia.

And Police will close to $300 million in new operating funding - its first significant boost in five years, most of which will go towards covering pay increases.

Corrections has also budgeted $5 million for the costs involved in it resuming management of Mt Eden Corrections Facility, after Serco's 10 year contract was cut short at 6 years.

Officials have been surprised by how fast the prison population has increased, and it is now forecast to reach 9800 by the end of the year. Just over $290 million of funding will be used by Corrections to deal with this increase.

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Corrections has struggled to cope with a rise in the number of criminals being deported from Australia, following a toughening of immigration laws there.

With 1000 deportees expected to arrive over five years, police have flagged the reoffending risk of that group, and Corrections has already made one-off grants to a service that provides support to deportees, some of whom have marginal links to New Zealand.

Corrections will get $12 million over four years to manage offenders returning from overseas.

Other new funding over four years includes:

• $8.8 to continue 24-hour GPS electronic monitoring for the highest-risk offenders and "improve the electronic monitoring assurance framework". The system has come under scrutiny following the case of Tony Robertson, who was being monitored when he murdered Blessie Gotingco.
• $20 million for out-of-gate reintegration services, which supports offenders as they leave prison and get used to life outside.

"Sorting out the basics such as accommodation, employment, education and training means offenders and improve the electric monitoring assurance framework," Corrections Minister Judith Collins said.

Budget 2016 will invest an extra $299.2 million in new Police operating funding over four years, including $49.2 million from a contingency in last year's Budget.

The Government has come under pressure after burglary resolution rates dropped into single figures in some areas.

The new operating funding over four years includes 280 million for police pay increases, and $8.2 million to develop the child protection offenders register.