Hospitals deferred thousands of operations as they prepared for a possible wave of Covid-19 cases - and to minimise contact under alert level 4.
The most urgent surgeries were still being done under the lockdown but elective surgery had largely been put off.
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Private Surgical Hospitals Association president Richard Whitney said, in many cases, the surgery was still badly needed, with some people living in pain or with deteriorating health.
Some cancer operations were among those being delayed, along with joint replacements or back, brain or gynaecological surgeries, he said.
Exact numbers were not yet available but 30,000 was a good estimate based on the normal workload of the private and public sectors, he said.
Around the start of the lockdown, almost all surgery was on hold to allow anaesthetists to train to work in intensive care units if they became overwhelmed by Covid-19 cases.
Cancer Society medical director Dr Chris Jackson says cancer operations have since increased but the extra safety protocols needed mean not as many can be done.
It was likely there had also been delays in diagnosis, partly because people had been avoiding general practices and emergency departments, he said.
While that was a worry, it had to be weighed against the fact that people with cancer were more susceptible to the virus, he said.
"It's complex because ... if you get to the situation ... where you have huge, terrible numbers of Covid in the community then that has a major negative impact on people with cancer," he said.
One of the key level 3 changes should be to ease current hospital restrictions on visitors - particularly to those who are dying.
"Being close to loved ones towards the end of life or during a critical illness is so important on a human level. And, that has been one of the hardest things of this lockdown," Jackson said.
Director-General of Health Dr Ashley Bloomfield said urgent diagnoses and surgeries would be the top priorities under alert level 3.
It would be a challenge, with hospitals already stretched before the virus, he said.
Bloomfield said DHBs were preparing to do as much as possible while keeping staff and patients safe from Covid-19.