New South Wales will be virtually debt free by the end of the financial year, the Treasurer says, but the Opposition argues that it will not last long.

Tomorrow's budget will confirm that on June 30 net debt is expected to be just 0.1 per cent of gross state product, or $663 million.

NSW Treasurer Gladys Berejiklian said that was the lowest of the mainland states.

"Our net debt position is virtually zero," Ms Berejiklian said.

"Against the backdrop of having zero debt, we are still spending record amounts on infrastructure, on those vital new hospitals, education, roads, and rail that the community needs," she said.

"This has been achieved through fiscal discipline and innovative policies such as asset recycling."

Yesterday the NSW Government announced that it would invest $560 million to help repair the state's foster care system.

The Government also announced the housing development across Sydney's west and south-west would be given a $262 million boost ahead of Tuesday's budget.

Opposition Treasury spokesman Ryan Park said the net debt result was driven by the privatisation of the electricity network and the debt free days would not last.

"When you've sold everything bar the kitchen sink and you're probably looking at selling that as well, you would expect at least some debt to be paid down," Mr Park said.

"Their biggest problem is going to be paying for health and education in the forward estimates, and their own intergenerational report indicates that the ability to generate the income needed to pay for those services is going to be difficult."

'This Government has gutted public service agencies'

Meanwhile, the State Opposition has been highlighting the amount of money the Government has been spending on private consultants, while at the same time slashing the budgets of government departments.

Labor analysis of papers tabled to parliament reveal the Government has spent about $150 million a year on consultants for the past two years.

Mr Park said the amount exceeded the total yearly budget of some government agencies, like the Office of Emergency Services, or the Office of Local Government.

"It's very clear that this Government has gutted public service agencies and now we are reliant on spending very large amounts on private consultants," Mr Park said.

"I would certainly like to see the Government ... get back to a situation where we have very good, strong, well trained public sector agencies and public sector advisors," he said.

"$3 million a week is being spent on private consultants, this is at a time when the Treasurer is asking frontline services, frontline agencies and frontline staff to rein in their expenditure - it doesn't make sense," he said.