A public health mobile Covid testing unit was currently on-site.
At least three elderly residents died during the March 2020 outbreak when 51 people contracted the virus in the St Margaret's cluster, including Waitakere Hospital nurses who treated sick elderly patients transferred into their care.
Hall said the Auckland Public Health Service confirmed late last night that a staff member had contracted the virus.
The staff member was already in precautionary self-isolation before taking a Covid test.
"We are grateful that this staff member immediately isolated, got tested and communicated to us so that we can swiftly manage this situation," said Hall.
Although staff members working alongside the infected employee in the unit were now in self-isolation, the hospital would ensure there were enough staff to continue to take care of all residents.
"We are taking direction from ARPHS and technical support from Waitematā DHB to stand up the extra processes and protocols needed to protect our residents, staff and community. We have sufficient PPE supplies and staff levels to ensure we can continue providing the best quality care we can," said Hall.
"This is a distressing time for the staff, residents and their families, however we are keeping calm and focused on doing everything we can to keep everyone safe and well."