The cases are in Lautoka and Nadi in the west of the main island, Viti Levu, and the settlement of Makoi, near the capital Suva.
The permanent secretary of health, James Fong, urged people to stay home.
"The virus is very much present in the community," Dr Fong said.
At a news conference late on Friday night, he said people should assume there is Covid-19 in the community, with cases of unknown origin rising daily.
The government has also announced that it is taking over several hotels in Suva to use as quarantine facilities.