Waitākere Hospital's emergency department was visited on Thursday by a person who later tested positive for Covid-19.
A Waitematā District Health Board spokesperson said the person had turned up to the West Auckland hospital with Covid symptoms.
They were "appropriately streamed" when they arrived and put into a separate area for people with symptoms of the virus, who are also kept separate from one another.
The DHB said the person was moved to a negative pressure room but is now in MIQ following their positive test.
A "small number" of patients in the separate area will be monitored and tested, although the person had no direct contact with them.
Although a small number of staff had contact with the person, they were all wearing full PPE and are fully vaccinated.
This means the risk to staff is considered low.
The DHB spokesperson said the Auckland Regional Public Health Service (ARPHS) had advised it the overall exposure risk is low.
The Ministry of Health said interviews were underway with the person to find out how they were linked to the current outbreak.
It said less than 10 patients were affected by the case. Although some had been discharged, they were being followed up by public health staff.
1News understands ambulances to the hospital were diverted for a short time as a result and part of the ED was cleaned.
The hospital never closed, with the ED still open to walk-ins. Other services were also still operational.