The spike in cases stems from "community spread," and not a single decision to reopen part of the state's economy, she said. Though there were recent spikes in Ocean County and in higher education institutions, she added, the increase is "widespread" across the state.
A review of cases that excluded schools and congregant living health care facilities, showed the biggest share of outbreaks stem from gatherings and parties, as well as day care and on farms, she said.
Related: Cuomo, de Blasio anticipate changes to COVID cluster restrictions
Democratic Gov. Phil Murphy advised residents to continue to use masks, keep social distance and quarantine if exposed to the virus.
"I would just plead with people to use common sense," he said.
New Jersey's cases have also reached the level at which the state travelers from other states with high COVID-19 levels must quarantine.
Murphy advised residents "not to travel, frankly," but said essential travel for work would be OK.
Related: Trump dismisses COVID-19 pandemic, rips Fauci
The quarantine, which New Jersey adopted along with New York and Connecticut, applies to states with a positive test rate higher than 10 per 100,000 residents on a seven-day average, or with a 10% or higher positivity rate over seven days.
On Monday, Murphy reported about 1,200 new cases overnight, putting the overall figure at 223,000. There were four deaths reported overnight, leaving the toll at 1,425.
For most people, the virus causes mild or moderate symptoms. Older adults and people with existing health problems are at higher risk of more severe illness or death.
MORE CORONAVIRUS COVID-19 COVERAGE
How coronavirus changed the New York region
Do you have coronavirus symptoms?
New York, New Jersey, Connecticut out-of-state travelers quarantine list
COVID-19 Help, Information. Stimulus and Business Updates
UPDATES
New York City
New Jersey
Long Island
Westchester and Hudson Valley
Connecticut
Centers for Disease Control and Prevention on coronavirus
Submit a News Tip