N.Y. MHY. LAW § 9.41 : NY Code - Section 9.41: Emergency admissions for immediate observation, care, and treatment; powers of certain peace officers and police officers

Any  peace officer, when acting pursuant to his or her special duties,
  or police officer who  is  a  member  of  the  state  police  or  of  an
  authorized  police  department or force or of a sheriff's department may
  take into custody any person who appears  to  be  mentally  ill  and  is
  conducting  himself  or herself in a manner which is likely to result in
  serious harm to the person  or  others.  Such  officer  may  direct  the
  removal of such person or remove him or her to any hospital specified in
  subdivision  (a)  of  section  9.39  or  any  comprehensive  psychiatric
  emergency program specified in subdivision  (a)  of  section  9.40,  or,
  pending  his  or  her  examination  or admission to any such hospital or
  program,  temporarily  detain  any  such  person  in  another  safe  and
  comfortable place, in which event, such officer shall immediately notify
  the  director  of  community  services  or, if there be none, the health
  officer of the city or county of such action.
    * NB Effective until July 1, 2012