Navajo Nation health officials say 58 reservation communities have uncontrolled spread of COVID-19.
They include Chinle, Ganado, Kayenta and Tuba City.
It comes as the tribe reports nearly 330 new known cases over a three-day period that ended Monday.
Officials say two deaths from the virus were also confirmed. Ten Arizona counties, including Navajo, Apache and Coconino, are currently in a high level of community spread, according to the Centers for Disease Control and Prevention.
The agency recommends that people wear masks in public indoor spaces along with other precautions in areas of high transmission.
On the Navajo Nation, residents and visitors are required to wear masks in public.
COVID cases have generally been on the rise statewide since mid-April.