N.Y. Mental Hyg. Law § 9.41
Any peace officer, when acting pursuant to his 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 in a manner which is likely to result in serious harm to himself or others. "Likelihood to result in serious harm" shall mean (1) substantial risk of physical harm to himself as manifested by threats of or attempts at suicide or serious bodily harm or other conduct demonstrating that he is dangerous to himself, or (2) a substantial risk of physical harm to other persons as manifested by homicidal or other violent behavior by which others are placed in reasonable fear of serious physical harm. Such officer may direct the removal of such person or remove him to any hospital specified in subdivision (a) of section 9.39 or, pending his examination or admission to any such hospital, 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.
N.Y. Mental Hyg. Law § 9.41