Royal Bournemouth and Poole hospitals are restricting visitor numbers in an effort to control the vomiting and diarrhoea bug.
Bournemouth's lead infection control nurse, Paul Bolton, told people to only visit "if absolutely necessary".
Different wards have been shut at different times so it is advised people call for more information.
At Bournemouth the wards currently closed are two, three, nine, 22 and some areas are closed in ward 21, while at Poole the Kimmeridge ward has been closed.
Wards have been shut at two Dorset hospitals after confirmed cases of norovirus.