Northland District Health Board has confirmed seven patients are in isolation at Whangarei Hospital after a suspected outbreak of norovirus.
Three people caught the vomiting bug at the weekend, but on Monday another four became ill.
The board says doctors are waiting on test results that will show whether the bug is the highly contagious norovirus.
It says the outbreak has been contained to one ward, which is closed to further admissions.
Meanwhile, at Thames hospital: four patients and 15 staff have contracted norovirus since last Wednesday.