The Prime Minister says National would have known the shortfall in the health spend when they were in government.

Jacinda Ardern says there's a hole of around $10 billion - and that's one of the reasons why her Government cancelled planned tax cuts scheduled for this month.

"I would have thought a minister of health would probably know that," Ardern says.

Ardern says for National to claim they knew nothing about things like the mould at Middlemore Hospital is disingenuous.

"It is worse than we thought, when we look at the capital needs of hospitals and health in particular, [and] also the deficits DHBs are facing, it is worse than I anticipated."

She did not believe that former health minister Jonathan Coleman and National leader Simon Bridges were unaware of the capital underspending deficits DHBs faced.

"There's no way you could turn a blind eye to the deficits that everyone could see."

Ardern also says isn't fair to blame Middlemore Hospital's building problems on the current Government due to the sector's under-investment.

"Obviously the issue of mould in the walls of Middlemore Hospital has not just happened. This is an ongoing infrastructure problem.

"I think to squarely place it on our shoulders … doesn't resolve the problem and that's what we need to do, but also ignores the fact that we've had significant under-investment in our health system for a consecutive number of years," Ardern said this morning.

Simon Bridges is asked if the National government invested enough in health, especially in light of Middlemore Hospital being riddled with mould. (Mark Mitchell)

RNZ today reported that in addition to the mould and asbestos issues at the Auckland hospital, Middlemore was forced to use emergency generators for weeks at its busy Manukau SuperClinic after a major power failure.

RNZ was also told of a hospital-wide power cut at the site two months ago.

Health Minister David Clark met the DHB last week.

He said today the problems with the power supply were not raised but he would receive information today.

"They have indicated that they're going to get back to me today with some advice about how they're managing building issues into the future."

He has also requested an asset register across the entire health system.

Clark laid the blame with the former government, saying it had prioritised tax cuts for the wealthy.

Bridges said today the previous National government had known the Counties-Manukau board was seeking more money but was not aware of the specific problems at the hospital.

"We did what we could, we continued to raise investment in that area. Now it's another go, clearly there'll be more investment but they've [the Government] talked about billions and billions of dollars, let's see what they do."

The Government recently approved an extra $11.5 million of funding to repair problems relating to Middlemore's rotting timber, leaks and mould - bringing the total cost of that project to $27.5 million.

The Counties-Manukau DHB said it had also budgeted to spend $3 million between 2017 and 2022 to increase the resilience of the hospital's power supply.

The New Zealand Nurses Organisation last week said it was worried mould in some hospital walls could escape into the building and become airborne.

Middlemore's maternity ward was also being monitored in case asbestos used in its construction was disturbed.

The ward is considered vulnerable because it was not built to a strength that meets modern earthquake standards.