Authorities in New Jersey say an armed man is holed up in a restaurant across the street from Princeton University's campus.

Police say there are no known hostages in the Panera Bread, but it's not clear what sparked the standoff that began around 10 a.m. Tuesday.

Authorities had shut down Princeton's downtown area, and two campus buildings were evacuated as a precaution. Armed officers were staged outside the restaurant with their weapons drawn while negotiations continued.

No injuries have been reported. Panera Bead employees who were at another nearby eatery declined to comment on the unfolding standoff.

It wasn't immediately known if the gunman had any connection to the university. Classes are not in session at Princeton, which is on spring break.