"All patients and staff working in the two affected wards between 6.30am and 4.30pm on Sunday 5 September are currently being classed as close contacts until we have done further investigations," Counties Manukau health added.
The wards at the hospital in Ōtāhuhu have been closed to any new admissions.
Patients were being cared for as "Covid-exposed" by staff using personal protective equipment (PPE).
The district health board said staff routinely wore surgical masks and full PPE where required, but all staff in the two wards were stood down.
Those staff would now work with occupational health and ARPHS regarding risk and actions.
All emergency staff were routinely required to wear N95 masks and goggles and, as such, were being regarded now as casual contacts, not close contacts.
"Occupational Health is working with these staff and no one has been stood down," Counties Manukau Health added.
Director-general of health Dr Ashley Bloomfield said the Middlemore Hospital patient was not yet linked to any other cases, though everyone in his 10-person household was being interviewed.
Speaking at this afternoon's 4pm press conference with Prime Minister Jacinda Ardern, Bloomfield said he was confident there would be a link.
The man presented at Middlemore with symptoms that were not Covid-19 symptoms, and was then admitted to the "appropriate place" for those symptoms, Bloomfield said.
Bloomfield said he was not aware if hospital staff who interacted with the patient were wearing N95 masks
The man would have ideally been isolated from other patients on the ward the following day, when he was suspected of having Covid-19, Bloomfield added.
Earlier, the Herald reported a man at Middlemore tested positive for Covid-19, and it was understood he shared a room with three others at the Edmund Hillary Block surgical ward.
Deputy Prime Minister Grant Robertson said the Covid-positive person in Middlemore entered the hospital on an unrelated matter.
