Junior doctors say they are taking strike action because of the dangers of being overworked in hospitals.
Hundreds of appointments and surgeries have been cancelled as junior doctors began a two-day strike on Thursday - the second strike action in two weeks.
Resident medical officers - junior doctors - picketed outside hospitals in protest against work conditions and a proposed pay cut for trainees in psychiatry, radiation oncology, pathology, public health and general practice.
While most junior doctors had been offered a 20 percent pay rise by Health New Zealand / Te Whatu Ora, doctors in those specialities singled out would receive a 12 percent pay cut.
Health New Zealand said its new offer to junior doctors included an average pay rise of 18 percent.
It said it was disappointed the union continued to issue new strike notices, despite facilitation continuing and against the recommendation of the Employment Relations Authority.
Resident Doctors' Association president James Anderson said its more than 3000 members were working all week and then doing back-to-back shifts on the weekend.
"And that means over the course of seven days, they will clock up about 71.5 hours which is an interesting number because the legal maximum in our contract is 72 hours, so we get right up 71.5, there's a clause in their contract that says we should work towards 60 hours but we've never managed to get the employer close to that."
When Amy Miles entered medical school at 18, she expected to work hard. She did not expect her life as a registrar would be nothing but work.
"I've just been rostered 10 days in a row, including 8(am) til 10.30pm, both days on the weekend, so Saturday and Sunday, and this isn't including overtime which I always work," Miles said from the picket line at Wellington Hospital.
Fellow registrar Charlotte Su said the workload felt unsafe.
"Truck drivers, they only work 12-hour shifts, like that's the max, but we're working 15 hours at a time."
At Auckland City Hospital, neo-natal registrar Jack Mackie's next rotation is at Waitākere Hospital.
"The roster is less than half filled so I believe there's three or four registrars for seven to eight slots, if not more, so they've had to cut down their services and they've had to get senior doctors to cover night shifts."
Paediatric registrar Nina Su said her colleagues were quitting.
"At the end of day, what we really want is to make sure that New Zealand is not just a factory for doctors for Australia, because at the moment, we're talking to a lot of junior doctors, a lot medical students who are looking at exit strategies, whether they're going to leave health [sector] completely or just move to Australia."
Te Whatu Ora said hundreds of patients were affected by the strikes, with 700 elective procedures usually done every week-day.
Last week's 25-hour strike forced the cancellation of 200 operations and a further 189 outpatient clinics.
Many patients at Wellington Hospital on Thursday backed the doctors' stance.
"They shouldn't have to do this to get people to listen," one patient said.
"I have been in the system for 18 years and I wouldn't be here without people like them, so it's heart-breaking to see."
The other union representing junior doctors - the Specialty Trainees Organisation - settled its collective agreement with Te Whatu Ora a couple of months ago.
The Resident Doctors' Association claims, under the current offer to them, doctors with the same training and experience working side-by-side will be paid differently in some cases.
The strike ends at 8am on Saturday.
If a new agreement is not reached, a third strike has been called for 30 and 31 May.