An estimated 200 patients missed out on operations last week and hundreds more had appointments cancelled because of the junior doctors strike.
Much more disruption is expected this week as half the country's doctors - about 2500 - walk off the job for two days from 16 to 18 May.
The doctors were striking because about 600 of them were set to get a pay cut of up to 12 percent, even though most were due an increase of about 20 percent.
They were also taking issue with rosters that required them to work back-to-back 15-hour shifts over some weekends, as well as working that week.
Te Whatu Ora Health NZ said 75 operating theatre sessions were called off around the country during 25 hours of the strike, which likely affected about 200 patients.
A further 189 outpatient clinic sessions were cancelled, with Te Whatu Ora saying the number of patients per clinic varied so much it could not say exactly how many were impacted.
Chief people officer Andrew Slater said some other patients would have had their operations deferred in the lead-up to the industrial action, particularly if they were complex cases.
"As part of preparing for the strike, we needed to decompress the hospital in the days prior to keep our patients and staff safe over the affected days," he said.
The Resident Doctors' Association is one of two unions representing junior doctors so the impact of the strike varied around the country, depending on the concentration of members at each hospital.
Te Whatu Ora did not answer a query about which hospitals or services were most impacted.
But, last week staff at Waikato Hospital said it was badly affected and they were worried about safety ahead of this week's larger action.
Canterbury had also said it was calling off procedures.
Slater said in areas with a high number of doctors in the union, rosters were rearranged so high-risk and non-deferrable essential surgery and procedures could still go ahead.
He still hoped the strike would be called off but hospitals were making contingency plans.
Senior doctors and junior doctors from the other union would still be working and people should turn up for their appointments unless contacted directly, he said.
Emergency departments would remain open.
