Staff at Waikato Hospital are recovering from the disruption caused by a major IT outage for hours on Wednesday.

Health NZ said late on Wednesday evening that the problem - which began at 10.44am - had been fixed, but it was contining to monitor the situation.

Thames, Te Kūiti, Tokoroa and Taumarunui hospitals were also affected.

The health agency has not said what exactly caused the problem, which meant longer wait times in the emergency department, some delayed surgeries, and forced staff to revert to paper systems.

Staff told RNZ patient history was limited to paper reports and any recent AI transcribed reports could not be accessed.

It also took longer to get test results and paging systems did not work.

Health NZ said it delivered safe patient care throughout the day.

"Any impact to clinical systems is treated with the greatest urgency. We reverted to manual processes for a number of areas such as patient information tracking and results reporting. Urgent care, including our Emergency Department, was prioritised with additional resource in place."

It said it would contact patients whose planned appointments were postponed to reschedule.