Striking junior doctors say they will not back down and district health boards must withdraw planned clawbacks to their current terms and conditions.
About 3000 junior or resident doctors are on strike for 48 hours, which is affecting all DHBs apart from West Coast District Health Board, over a lack of progress in pay talks.
Strike action began at 7am.
Auckland Hospital has the most junior doctors of any in the country, and more than 30 were gathered outside the gates of Auckland Hospital by 9am, with numbers expected to grow to about 50.
Alyssa Page has worked at North Shore Hospital for the past three years and said she could be required to work consecutive 15-hour days over a 10-day period, and at times, a single doctor was made responsible for up to 200 patients.
"It starts to compromise the care that we can give and also our ability to make clear, clinical judgements," she said.
Auckland Hospital resident doctor Ry Tweedie-Cullen said it was not about money.
"There's a good number of people that have come out today to support maintaining the working rights we've got at the moment," he said.
"What we're really asking for is the ability to give the best care to the patients."
One protestor had worked a total of 28 hours over the weekend.
"Basically, after that much work and you're trying to get home, you're equivalent to a drunk driver," Dr Christina Vanderboor said.
She said they were consistently working over capacity for the emergency ward.
"It's pretty hectic, especially over the holiday period."
One of the doctors striking said she had just got off an 11-hour shift after finishing at about 2am in the emergency department and was very tired.
She said that's pretty reflective of what's going on with these junior doctors at the moment.
The placards that could be seen included 'all we ask for is a fair deal'; 'support junior doctors'; and 'tired doctors make mistakes'.
There was a lot of support for the junior doctors outside the hospital.
Cars were tooting, fists were being pumped in the air and people who were leaving the hospital were also supportive.
The doctors and their district health board employers are in conflict over pay and working conditions including rosters.
The doctors' union, the Resident Doctors' Association, said the strike action was over continued attempts by DHBs to claw back employment conditions.
That included aspects of safer hospital rosters for the doctors, agreed between the sides after strike action two years ago.
The doctors' current pay deal ceases to exist on 28 February, after which different conditions could be offered to doctors.
Resident Doctors' Association senior advocate David Munro said that was not acceptable and DHBs must return to talks and settle a fair deal.
"Doctors aren't going to back down, the strike action is going to continue and until the DHBs are prepared to withdraw those clawbacks, we are not going to see an improvement to the situation."
DHBs have struggled to implement the rosters but rejected the clawback claim, saying they simply wanted more flexibility.
DHBs spokesperson Dr Peter Bramley said they were very hopeful there would be an agreement before the expiration date.
"We are committed to meeting and committed to bargaining in good faith and from the DHB perspective convinced that there's every opportunity for us to find a constructive solution together."
Many non-urgent surgeries and outpatient clinics have been deferred or postponed during the 48-hour strike but a DHB spokesperson said the acute needs of patients would be met.
Ian Powell, executive director of senior doctors union the Association of Salaried Medical Specialists said it was a tense stand-off that could drag on for months.
"It will go into March unless there is some de-escalation, but at the moment the differences are so great that this has become a winner-takes-all dispute and it's very difficult to find a way through those disputes unless there is a lowering of those tensions.