N.Y.C. Admin. Code § 3-104: § 3-104 Declaration of emergency.

Whenever the mayor determines that there has been an act of violence or a flagrant and substantial defiance of or resistance to a lawful exercise of public authority, and that, partly on account thereof, there is reason to believe that there exists a clear and present danger of a riot or other general public disorder, widespread disobedience of the law, and substantial injury to persons or to property, all of which constitutes a threat to public peace or order and to the general welfare of the city or a part or parts thereof, the mayor may declare that a state of emergency exists within the city or any part of parts thereof.