National has vowed to spend an estimated $400 million to $500m to rebuild Hawke's Bay Hospital if it gets elected to Government.

But Labour Tukituki candidate Anna Lorck says while there is value in replacing the hospital's main building in time, but there are "far greater priorities" for investing into the hospital right now.

National Party leader Judith Collins, alongside spokesperson for health Dr Shane Reti and Tukituki MP Lawrence Yule, made the campaign promise at the hospital on Tuesday.

The budget for the project would include a $7m immediate installation of air conditioning, and an expansion of the emergency department.

The hospital's main block was built in 1961 and despite some modernisation and earthquake strengthening was "outdated and barely fit for purpose", Collins said.

Under a National Government design work on the rebuild would begin in 2021 with the aim to have diggers on site in 2025.

The emergency department would also be expanded to better cater for current needs and future growth.

The hospital currently has no air conditioning which prompted complaints from both staff and patients in recent summers.

Under National, installation of air-conditioning would begin immediately and had been identified as an "urgent" project which could not wait for the rebuild, Collins said.

Yule said he had advocated for the upgrades since entering parliament in 2017.

"I'm proud of National's commitment to the district. This investment in Hawke's Bay Hospital, combined with the already announced $300 million roading investment, is the largest ever investment in the Hawke's Bay region," he said.

He believes one hospital is enough to service Hawke's Bay but said there are some "pinch points" such as the ED and Intensive Care Unit being too small.

"I think most Hawke's Bay residents would think this is past it's use-by-date and needs to be replaced."

National's Health spokesperson Shane Reti said Hawke's Bay was a rapidly growing part of New Zealand, and the hospital needed to grow to match this.

Lorck, who is on the DHB's board, said National's plan to install air conditioning, only to knock down the building a few years later, shows "they are not planning nor thinking about where our health money is best invested for saving lives".

She said there were other issues which needed to be prioritised.

"Priorities like an interventional cardiology centre so we can get lifesaving heart procedures done here at our hospital and avoid people having to go out of the region, along with building more operating capacity for elective surgery," Lorck said.

"Under Labour we're making the greatest investment into our hospital in over a decade with new radiology, surgery expansion and building a new operating theatre along with improving access to faster cancer treatments."

A Hawke's Bay DHB spokeswoman said they could not provide comment to policy or infrastructure announcements by any political party during the election process.