When an emergency exists involving the immediate preservation of the public peace, health or safety, an ordinance may be passed which shall be effective immediately: Provided; That such emergency and the facts creating the same shall be stated in one section of the bill; and Provided further; That such bill shall not become an ordinance unless on its final passage by the City Council at least a majority plus one of all the members of the Council vote in its favor, and it shall have been approved by the Mayor.