The mandate will take effect next Wednesday and cover seven counties, representing more than 55 percent of the state's population.
"I will be instituting a requirement to wear face coverings while in indoor public spaces, such as grocery stores and other businesses, for the following counties: Multnomah, Washington, Clackamas, Hood River, Marion, Polk and Lincoln," Brown said.
The move comes after a pause in Oregon's reopening process last week, which Brown said was instituted to give public health experts time to assess what was causing a recent rise in COVID-19 cases in both rural and urban communities.
At least 278 new cases were reported in the state Tuesday, and nine of the past 11 days have seen new infections in the state surpass 100, according to The Oregonian. One hundred nineteen of those new cases were from a single outbreak tied to a local church.
The Oregon Health Authority has continued to analyze the state's data, including the likely sources of the growth of new cases, as well as hospitalizations, results in contact tracing, and other metrics, Brown said.
The entire tri-county region of Multnomah, Washington, and Clackamas will remain in Phase 1 for at least 21 days before they will be eligible for Phase 2, the governor said.
"I know this impacts communities and businesses in Clackamas and Washington counties but, as we reopen our state, we must recognize how interconnected the metro area is," she said. “The next few weeks will be difficult, and we will be monitoring the data regularly. We are much better prepared than we were in early March. We have increased PPE, much more widespread testing, and many more contact tracers.
“However, if hospitalizations spike too rapidly if the capacity of our health care system is threatened, we will be forced to revert to stricter rules," Brown added.
She did move to allow Marion, Polk, and Hood River counties to begin their Phase 2 opening process Friday. Marion and Polk counties saw a recent decline in COVID-19 hospitalizations, and all three counties "implemented timely follow-up on cases in the past week," she added.
Oregon Gov. Kate Brown speaks at a news conference in Portland, Ore, March 16, 2020. The Oregon Supreme Court has upheld the governor’s shutdown orders aimed at preventing the spread of the coronavirus. (Associated Press)
Separately, health officials in Lincoln County issued a directive Tuesday requiring all residents to wear face coverings in both indoors and outdoor public spaces where social distancing of approximately six feet can't be maintained.
Bars, restaurants and other eating establishments operating under Oregon's phased reopening guidelines will be exempt from the separate Tuesday order, authorized by Lincoln County’s health officer and public health administrator.
Brown and health officials previously recommended that masks be worn in public, but it wasn't a requirement until the seven-county mandate takes effect next week, the paper reported.
The federal Centers for Disease Control and Prevention (CDC) has advised people in the U.S. to wear face coverings in public settings, such as grocery stores, pharmacies and gas stations, whenever other social distancing measures are difficult to maintain.
"Cloth face coverings may slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others," the agency says on its website.
Oregon has seen more than 6,218 confirmed coronavirus cases and at least 183 deaths from the virus, according to data from Johns Hopkins University.