Earlier in the day, the authorities said there was one case in Moorea and one in Tahiti.
In an updated statement, the government said a third had been confirmed Thursday.
The individual is reported to be a European tourist who arrived two days ago.
Last week, the first tourist was hospitalised with the virus after falling ill on the atoll of Fakarava.
The French High Commissioner Dominique Sorain said access will be tightened and only residents are now allowed to enter French Polynesia.