They say many others, including staff members, are infected and are being treated on site.
The facility has been placed on lockdown and will not accept additional patients or allow visitation, and the state health department is involved.
"We cannot stress enough the need to remain calm, practice social distancing, work from home and be vigilant," Mayor Dan Mahler.
MORE CORONAVIRUS COVID-19 COVERAGE
Frequently Asked Questions
Where are the testing centers
See how our communities are making a difference
Free educational resources for parents and children
How you can help victims of coronavirus
Where is COVID-19 now? and other resources
Coronavirus news and live updates in New York
Coronavirus news and live updates in New Jersey
Coronavirus news and live updates in Connecticut
New York City updates
Long Island updates
How coronavirus is leaving ghost towns in its path
Coronavirus prevention: how clean are your hands?
Social distancing: What is it and how does it stop the spread of coronavirus?
Coronavirus closures and cancelations
Coronavirus tips: What Americans need to know
Related Information
Centers for Disease Control and Prevention on coronavirus
New Jersey Department of Health
John Hopkins' coronavirus tracking dashboard