Eleven patients have been isolated at Whangārei Hospital after a suspected norovirus outbreak.
The ward, for elective and acute orthopaedic and multi-trauma patients, has been closed to new admissions and visitors will be restricted.
The Northland District Health Board said strict control measures were in place.
It said norovirus was currently widespread in the community, and symptoms included vomiting, diarrhoea and stomach pains.