Mowi has reported a suspected case of infectious salmon anaemia (ISA) at its Kveitskjeret farming site in Frøya.
The suspicion was notified to the Norwegian Food Safety Authority on 20 April following positive PCR test results from samples taken at the site.
Authorities said further samples would be collected and sent to Norwegian Veterinary Institute for confirmation of the diagnosis.
Restrictions have been imposed on the site to limit any potential spread of infection, including a ban on moving fish without specific approval.