Four patients tested positive for COVID-19 at Collingwood General and Marine Hospital, prompting an outbreak to be declared.
The hospital says the infected patients in the medical unit have been isolated, and contract tracing is underway.
All other patients are being swabbed to test for the virus.
The unit is closed to visitors, except for palliative and end-of-life patients.
Enhanced cleaning measures have been implemented.
A release from the hospital stated it is working with the health unit to control the outbreak.