Ordinances passed as emergency measures or measures necessary for the immediate preservation of the public peace, health or safety shall be subject to referendum in like manner as other ordinances except that they shall go into effect at the time indicated in such ordinances. If, when submitted to a vote of the electors, an emergency measure is not approved by a majority voting thereon, it shall be considered repealed as regards any further action thereunder; but such measure so repealed shall be deemed sufficient authority for payment in accordance with the ordinance, of any expense incurred previous to the referendum vote thereon.