An emergency ordinance is an ordinance which, in the judgment of the city council, is necessary for the immediate preservation of peace, health, or safety, and which should become effective prior to the time when an ordinary ordinance would become effective. Every such ordinance shall contain, as a part of its title, the words, "and declare an emergency"; and in a separate section, herein called the emergency section, shall declare the emergency, and state the reasons why it is necessary that the measure become effective immediately. An affirmative vote of at least three-fourths (3/4) of the councilmembers shall be required for the passage of an emergency ordinance. An emergency ordinance shall take effect immediately upon passage and publication.