Work's going on to strengthen building plans and oversight at the redevelopment of three regional hospitals in the North Island amid "significant issues".

However, Health New Zealand says it has no concerns about the projects.

A Treasury report in December rated the Tauranga, Hawke's Bay and Palmerston North projects 'amber' on a scale of 'green-amber-red'.

It said all three projects - which are at design and early works stage - were feasible but were rated amber as they had "significant issues that need to be addressed to enable confidence in delivery and benefits realisation". These were around what the projects were aimed at and the options to deliver that, engaging partners and oversight - as well as clinical services planning at Hawke's Bay and Palmerston North.

Health NZ told RNZ they were all still rated amber.

"All three projects remain rated amber while work continues to strengthen their programme business cases and governance processes ahead of future decision-making and approvals," head of infrastructure planning and investment Aaron Matthews said.

"The amber rating does not reflect a single critical issue.

"Rather, it recognises that several areas, including strategic planning, stakeholder engagement, governance and supporting evidence, require further development as these complex programmes mature."

Hawke's Bay and Palmerston North were still gathering evidence to back the rationale for what to build, but this "does not in itself reduce or expand project scope".

The regional hospitals have struggled for years with old buildings that are too small and increasingly not fit for purpose, and some of them with earthquake risks.

"The issues identified do not indicate wider problems with the regional hospital redevelopment programme," said Matthews in a statement.

The three scrutinised in the Treasury report are in either their first or second stages - often there are four stages in a big project.

The Budget in May put some money into the design, plans and early site works for the three due to be done by either this financial year or 2027-28.

Delays have included at least a year for the $460m stage two work at Taranaki base hospital.

Health NZ said it had upped oversight and quality checks (assurance) across its big projects.