Seriously ill cancer patients could be sent to Australia for treatment as Waikato District Health Board wrestles with a crippling cyber-attack and potential privacy breach.

A senior doctor says the malicious ransomware attack is putting scores of lives at risk and the Government must intervene to protect patients who are missing out on vital treatment.

The doctor, who the Herald agreed not to name, works in Waikato Hospital's cancer centre.

They said the situation was a national health crisis and far worse than the DHB was making out.

A group claiming responsibility for the attack yesterday claimed it had accessed confidential patient notes, staff details and financial information.

They said the DHB had until today to comply with its demands or warned the information would be made public.

"We stole documents ... We have a lot of personal info of employees and patients, financial information etc," the emailer said.

"We give them 1 more chance to contact us. 1 more day."

The DHB's entire system crashed on Tuesday last week during a cyber-attack described as "the biggest in New Zealand's history".

Some surgeries and clinics at the DHB's five hospitals have been postponed and non-urgent cases are being asked to stay away from emergency departments. Experts are scrambling to get the system up and running but any fix is unlikely till at least next week.

The cancer service is among key healthcare services heavily impacted, with hundreds of cancer patients unable to have vital operations or access radiotherapy treatment, the doctor said.

Staff had been told to prepare for the centre being out of action for at least a month, and fear there is no plan in place for the growing number of affected patients.

"We are a huge cancer centre and essentially we are down."

The DHB had arranged for the most urgent patients to be seen by private providers in Tauranga and, from next week, Wellington, the doctor said. Nurses and clinicians were accompanying patients to provide care.

Auckland Hospital had agreed to treat Waikato DHB's emergency cancer patients who could suffer major consequences such as being paralysed if treatment wasn't given, but it had no capacity to take anybody else, the doctor said.

An Auckland DHB spokeswoman confirmed the hospital was caring for Waikato's most urgent radiotherapy patients.

"We're assisting wherever possible".

The Waikato doctor said other national radiotherapy treatment centres were full and staff were now seriously discussing whether patients should be flown to Australia.

"When you've got patients who are on treatment or due to start treatment - people with tumours that are growing - you've got to be able to send them somewhere else because we just don't know when we can start them here."

Waikato DHB said earlier this week that 17 urgent patients were being transferred to Tauranga Hospital to continue treatment.

But the doctor said another 70 patients should be receiving treatment now but weren't getting it.

There appeared to be no plan for a further 100 patients due to start radiotherapy within the next three weeks, 60 new patients seen in the past two weeks requiring radiotherapy planning, and 145 patients still waiting to be seen by a radiation oncologist, the doctor said.

Depending on the cancer, radiotherapy treatment could be required five days a week for up to seven weeks.

Waikato DHB provided cancer treatment for the Waikato, but also Lakes DHB and Tairawhiti DHB.

The doctor said staff didn't know who was on their waiting list as they were locked out of the hospital's IT system.

The only technology available to them was their own personal laptops and email.

They couldn't access patient information, old scans or look at blood tests.

Staff were instead having to track down patients using paper copies of consent forms and had been warned the disruption could last for a month.

Patients requiring only chemotherapy could still be treated due to prescriptions being able to be handwritten.

"I don't know why there's this unwillingness to recognise or at least put it out in the media what a problem it is," they said.

"We are scrambling."

Waikato DHB executive director hospital and community services Chris Lowry said they were concerned about radiation therapy services and providing it to patients currently undergoing treatment, as well as how to manage any new referrals into the system while the Waikato centre was out of action.

The DHB was working with private providers first as there was limited capacity at the public hospitals.

Lowry said clinical teams had suggested sending some patients to Australia but the DHB wanted to ensure it was using all available space in other domestic cancer centres before exploring that option.

Waikato DHB chief executive Kevin Snee denied the DHB was downplaying the problem and said there were significant cancer care issues.

Other services such as the emergency department were taking longer to do things due to adopting manual processes.

"Obviously all of our services are not working as normal ... These services are trying really hard to deliver the best possible care for patients in really trying circumstances."

Snee said the DHB was getting good support from the Government.

Shelley Campbell, chief executive of Waikato/Bay of Plenty Cancer Society, said the loss of systems had been hugely disruptive for cancer patients, with many feeling anxious about treatment delays.

Health Minister Andrew Little told the Herald last night: "I am aware some journalists have received what appears to be personal and patient information stolen from the Waikato District Health Board in the ransomware attack.

"Ransomware attacks are a crime. The New Zealand Government will not pay ransoms to criminals because this will encourage further offending."

Patient wellbeing and supporting staff remained the Government's first priority.

"I have been in touch with the Waikato DHB Commissioner Dame Karen Poutasi this evening and will continue to be in contact with her about any assistance the DHB requires to support people whose information may have been held in the DHB's systems."

Anyone in the Waikato region who is concerned about their personal information could contact the DHB special response line 0800 561 234 which opens again at 8.30am.

Anyone who needs to talk can call or text 1737 at any time.

"There is an active police investigation. Other agencies such as the NCSC and the Privacy Commissioner continue to support the DHB."