About 30,000 nurses across the country have started strike action today for eight hours, in protest against pay and working conditions.
It comes after failed negotiations in which nurses voted on Monday to go ahead with the strike, rejecting a revised pay offer from district health boards.
Nearly all non-urgent surgery and outpatient clinics have been cancelled today.
Emergency services will still run today and those with urgent medical needs are being told they will still be able to attend hospital or dial 111.
GPs and Healthline will also be available throughout the day.
Spokesman for all the DHBs, Jim Green, said most non-acute and elective procedures had been cancelled, "to reduce demand on services and reduce patient numbers as much as possible before the strike".
"These will be deferred on the day of the strike to enable us to focus on those for whom hospital care is the only option during the strike."
But the Government's vaccination roll-out plan will take a hit.
Auckland District Health Board confirmed only two vaccination centres will open, with the lack of available nurses prompting safety concerns.
"Due to strike action, the majority of our metro Auckland community vaccination centres will be temporarily closed on Wednesday," the DHB said in a statement.
"Without enough registered clinical staff on site we can't administer the vaccine safely at these sites. Bookings at the sites have been moved to other days so that no one misses out."
The Ministry of Health has not confirmed what is happening with other vaccination centres across the country, although it will depend on whether those staffing them are members of the union organising the strike.
What is planned for the day
In Te Whanganui-a-Tara, nurses will gather in Civic Square before heading to Parliament; in Tamaki Makaurau, the strikers will march down Queen St; Kirikiriroa to Garden Place, and Otepoti, to the Octagon.
Across all 20 DHBs, members of the New Zealand Nurses Organisation will stop work, and head out to join the picket lines and marches.
Health care assistant at Matariki Hospital, Rhonda Hare, will be in Te Awamutu, just south of Hamilton.
"We've got music playing, we've got our wigs and everything else," she said. "We're walking out front, having donuts, hot coffee, pizzas," she said.
"And then we're walking up the main street of Te Awamutu - up one side and down the other [just] making the public aware of what goes on at Matariki - how short [of staff] we are in order to do our work properly."
Council of Trade Unions president Richard Wagstaff said nurses were being fully supported by their affiliate unions, including the 70,000 other unionised medical professionals.
"The Trade Union movement is right behind the nurses in taking this action.
"We recognise that they're taking the stand because of the very serious issues that they're facing on the job every day.
"We're right behind them. We know they do an incredible job for New Zealand and they need the support of everyone including the union movement."
Staff numbers dispute
Meanwhile, the nurses union has alleged some DHBs have requested more cover to keep life-preserving services going than would usually be rostered on.
In Parliament yesterday, when asked about it by Green Party MP Dr Elizabeth Kerekere, Health Minister Andrew Little denied it.
"I'm advised that no district health boards have asked for more staff rostered for life-preserving services during the strike than would normally be on a roster.
"In fact, many areas asked for just one fifth of normal numbers."
Green said he strongly rejected any allegation DHBs were seeking more cover than usual.
But the Nurses Organisation's industrial services manager, Glenda Alexander, said that was not the message she was getting from members.
"They're pretty accurate at knowing the real effect of who's on the floor and who's not on the floor at any given time.
"They've told us very clearly that there are numbers of people who will be on duty during the hours of 11 and 7 that, in many places, are higher than the usual places.
"Also we do have at least one of the adjudications on the matter that clearly says there were going to be more people there than usual."
The NZNO has agreed, under an emergency management protocol, to have a pool of nurses who would respond to need.
Alexander said yesterday a number of DHB's suddenly asked for last-minute extra cover.
"It's kind of interesting it's a bit pre-emptive.
"The situation has changed already and the strike hasn't started. I guess we try and take them in good faith that they are providing us with proper projections of what demand will be there tomorrow."
Canterbury DHB said thanks to early notice of the strike, around 60 operations had either been brought forward or postponed.
Alexander said an effort to reduce today's demand hasn't been made by all DHBs.