A bigger prison and more front-line police officers are some of the key Budget announcements that those working at the coalface of the country's justice system are hoping to see confirmed.

Corrections Association of New Zealand president Alan Whitley said there was one big-ticket item that needed to addressed in the Budget - a final decision to build an upgraded Waikeria prison to its full capacity.

Whitley said the association's members had been working in "atrocious" conditions and that some areas of the prison were closed due to black mould or structural issues.

"The prison was built in 1910 - it's archaic. It's not somewhere you should be trying to rehabilitate prisoners.

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"It's just not a place we should be housing prisoners - let alone having people working."

It was supposed to be closed in 2012, and then again in 2015, Whitley said.

A big concern for people working there now was the uncertainty, he said.

"If the new prison is not being built, they are just going to be worried that they are going to close that prison and that there will be more redundancies."

A modern facility would allow for better means of segregating prisoners away from each other and away from staff, he said.

"It's a better rehabilitative environment as well."

New Zealand Police Association president Chris Cahill said the Government had promised 1800 police officers and they were pretty convinced that figure would be confirmed in the budget.

"It will make a real difference. It's a large increase that we are really appreciative of."

They wanted to see the number confirmed and hoped to see that those extra police officers would be fully funded, he said.

"There's no point in giving them if they are not going to fund them properly because that will just be a drain on operational policing."

Hand in hand with that figure, there would need to be more support staff to ensure that those 1800 were successful, Cahill said.

The police had faced an increase in demand but no increase in staff, he said.

"Ten per cent year on year around family violence, mental health callouts - all those sorts of things," he said.

"We really need to get front-line staff out there on the street and make sure that it's fully funded and that they are going to keep it coming over the next three years."

The organisation was keen to see what kind of commitment would be made to mental health services in the Budget, he said.

"Up to 20 per cent of front-line officers' time is spent on mental health callouts," Cahill said.

"A lot of the time these people shouldn't really be interacting with police, they should be interacting with mental health services but there just isn't the quantity of those services - especially in provincial New Zealand."

The Police Association was pleased to see the announced boost in funding for family violence services which would get a 30 per cent increase in total funding of $76.2 million more over four years.

The raise was announced by Prime Minister Jacinda Ardern at a Salvation Army event in Wellington last week.

"It's all well and good for police to deal with what is happening at the immediate time but there needs to be those other government resources that can come in and fix the long-term issues for those families," Cahill said.