Giuliani has police out to make sure vendors don't take advantage of the current situation. All non-essential personnel are asked to NOT enter the city. People are asked to stay home unless absolutely 100% necessary to attend work. Bridges are partially open, all going OUT of the city, no entry. (thanks to ArthurQ for info!)
http://www.theregister.co.uk/content/57/21615.html - list of businesses in the WTC
New York Port Authority says city will be open above 14th Street