Up to 3000 junior doctors are walking off the job on a two-day strike from all public hospitals that kicked in at 7am.
They won't be back at work until 7am Thursday as they demand their 12-in-a-row day shifts be reduced to 10 and seven-in-a-row night shift roster cut to four.
Several hundred junior doctors will still work providing life-preserving cover and around 300 non-union member colleagues will also be at work, along with nurses, assisting senior doctors who'll hold the fort.
Essential services like emergency departments, emergency surgery and maternity care will continue, but non-urgent operations and appointments will be rescheduled.
Junior doctors, known as resident doctors, last went on strike in 2008.
Their union, the New Zealand Resident Doctors' Association, says they're not for turning.
"We're under instruction that if we don't get this settled in negotiations after the strike then we're to proceed with further strike action," said Deborah Powell of the association.
But the DHBs and others argue what's being demanded is unreasonable.
"We're happy with the junior doctors working shorter shifts. We're just simply saying if you're not working 12 days we wouldn't pay you for 12 days," said Prime Minister John Key.
It's all a headache for the country's 20 DHBs, but they've spent the past fortnight in high-level contingency planning and are reassuring New Zealanders they'll still get safe care during the strike.
"I'm comfortable having talked to each of the DHBs this morning that they're as prepared as they can be right now," said Anne Aitcheson, DHB national contingency planner.
Adding to the DHBs' stress is news the senior doctors union's not happy with the $180 to $500 hourly rate, in addition to their base salary, most DHBs are offering senior medics to cover during the strike.
The union wants that rate, struck at the 2008 junior doctors' strikes, inflation adjusted, but the DHBs have said no. Despite this, senior doctors will still work.