The county, which is on the state's border with Mexico, is seeing an exceptionally high positivity rate, or the proportion of people being tested that return a positive result for COVID-19. The 14-day average positivity rate is approaching 23% in Imperial County, Newsom warned.
For reference, the seven-day positivity rate in California as a whole is 5.7%.
WATCH LIST: Counties where COVID-19 is getting worse
About 500 patients have had to be transferred out of overflowing hospitals in Imperial County to receive treatment elsewhere, Newsom said.
He said county officials are meeting over the next several days to discuss how to tackle the issue. For now, he is just advising them to take action.
"We are advising and counseling them to move forward and reinstitute the stay-at-home order," Newsom said. "But they will move at their discretion."
If they fail to come up with a plan, he said, he will take action.
"If they are not able to come to some consensus, I am committed to intervening, as is my role and responsibility as governor in the state of California."
Newsom has returned to more regular briefings over the past week, as the state has seen a stunning surge in the COVID-19 crisis.
The latest statewide figures show:
RELATED: New COVID-19 cases in California rise 69% in 2 days, Gov. Gavin Newsom says
On Thursday, Newsom unveiled a new forecasting site, which he called "a model of all models." The state's forecast shows statewide hospitalizations more than tripling over the next month, if current trends continue.
The rise in COVID-19 cases follows weeks of reopening around the state. Most of California is now in Phase 3 of the governor's reopening plan - the final phase before concerts, festivals, conventions and the like are allowed.
Newsom said he is prepared to "revert back" to more stringent coronavirus restrictions, if necessary, but hopes we won't have to.
"We don't intend to do that, we don't want to do that, but I want to make this clear - we are prepared to do that if we must," Newsom said. "Clearly we have the capacity, individual and collective capacity, not to have to go in that direction by just being a little bit more thoughtful about how we go about our day-to-day lives."
WATCH: Here's a breakdown of Newsom's four stage plan to reopening California