Grant Robertson says the instance of a patient in a surgical ward at Middlemore Hospital in Auckland who tested positive for Covid-19 is "clearly disturbing".
A person who shared a room with three others in the hospital's Edmund Hillary block ward later tested positive for Covid-19.
The man was admitted to the ward at 7am on Sunday, displaying Covid-19 symptoms. He tested positive for the coronavirus later that day.
An employee at the hospital confirmed the case to 1 NEWS on Sunday evening.
On Monday morning Deputy Prime Minister Grant Robertson confirmed to Breakfast that the patient entered the hospital on an unrelated matter and then tested positive for Covid-19.
"Clearly for the people in the room this is disturbing," Robertson said.
All other patients on the ward will be tested and go into isolation, he said.
Robertson told Breakfast hospital staff were wearing full PPE. They are isolating and will be tested for Covid-19.
Health authorities will look to find out more information about the breakdown in Covid-19 protocol, he said.