Whenever there are urgent reasons for the filling of a vacancy in any position in the police force and there are no names on the eligible list for such appointment, the appointing officer or body may nominate a person to the commission for noncompetitive examination and if such nominee shall be certified by the commission as qualified after such noncompetitive examination he may be appointed provisionally to fill such vacancy. It shall thereupon become the duty of the commission within three weeks to hold a competitive examination and certify a list of eligibles, and a regular appointment shall then be made from the name or names submitted by the commission: Provided, however, That nothing herein contained shall prevent the appointment without examination of persons temporarily as police officers in emergency cases for the suppression of riots, tumults in times of war, pestilence, conflagration or public celebration.