The Waikato District Health Board (DHB) warns the aftermath of the cyber attack on its systems is "not going to be resolved quickly".
The DHB's computers were targeted in a ransomware attack a week ago, believed to have been triggered when someone opened an attachment they shouldn't have.
The group claiming responsibility says it has obtained the personal information of patients and employees. Newshub has been sent what are claimed to be documents stolen in the hack.
On Wednesday the DHB provided an update, saying there is an "ongoing criminal investigation".
"We are aware that the media have received what appears to be personal and patient information from Waikato DHB information systems," it said.
"Waikato DHB are working closely with the National Cyber Security Centre, Government Communications Security Bureau (GCSB), the Privacy Commission and NZ Police to respond, remediate and recover from this incident."
Due to the complexity of the incident, chief executive Dr Kevin Snee says the situation is not going to be resolved quickly.
"Our staff are pulling together as a team and working collaboratively with our partners to restore services, but disruptions are to be expected as workarounds are put in place."
Cancer patients transferred around NZ
Waikato DHB says cancer patients are being transferred around the country for treatment while its IT systems are restored.
Dr Snee has previously said getting everything back online has taken longer than first expected and it could be weeks before services are restored back to normal.
In a statement on Wednesday, Waikato DHB's radiation oncology service said it is working with cancer care providers in the North Island to ensure patients continue receiving treatment.
"There is considerable pressure on the system at the moment, but staff at Waikato Hospital are working hard in unique circumstances to ensure patient safety and care remains at the forefront," radiation oncology clinical director Dr Cristian Hartopeneau said.
Seventy patients were on treatment at the time of the incident. Three patients have been transferred to Auckland DHB for urgent care, and 18 clinically prioritised patients have been seen at either the Kathleen Kilgour Centre in Tauranga or the Bowen Icon Cancer Centre in Wellington.
The rest are in the process of being seen either this week or the following week.
Waikato DHB adds New Zealand and Australia have a long-standing arrangement to transfer patients for treatment, but this is only a last resort.
"I also appreciate the support of our partners, which has been vital to ensure we can provide the people of the Waikato with confidence to access the health services they need," Dr Snee says.
"This is a criminal investigation and we have every confidence that it is being dealt with by NZ Police and cyber security experts. Care and safety of patients remains our highest priority, and we must concentrate on health services and supporting our staff to do their job."
