That would likely be the case in some other hospitals, but Te Whatu Ora chief of people Andrew Slater said the agency would not know the full impact until after the strike had finished.
Health services would still be available for those who needed them, he said.
Senior doctors and junior doctors from the other main union would still be working, and would be providing essential “life-preserving” services.
The doctors taking industrial action are members of the Resident Doctors Association.
Senior advocate Melissa Dobbyn said they worked right across the country and in every speciality.
They range from those just out of medical school, to those about to become specialists.
Most were due for a pay rise of about 20 per cent in their latest contract, but said they were striking to support a smaller group in line for a pay cut.
One of the doctors, Dr Rosa Tobin Stickings, told First Up the current pay offer was not good enough and they couldn’t accept pay cuts for any union members.
Tobin-Stickings, who is training to be an emergency registrar, said with 500 resident doctors short across the country, shifts were getting “harder and harder”.
It was not unusual to start work and be told she had to cover for another doctor.
“It’s exhausting to be working in this environment and we’ve been working in this environment for some years ... and we’re getting pretty burnt out.”
Sometimes, the doctors had to apply for annual leave a year in advance and it was difficult to get leave for education purposes or to attend conferences to help with their training.
Many junior doctors had enormous leave balances and so far Te Whatu Ora had not responded to how leave pressures could be improved, she said.
A second two-day strike is planned from May 16, and the union would take a vote on further action, Dobbyn said.
