It shall be unlawful for the owner or operator of a motor vehicle to drive to, leave such vehicle standing, whether attended or unattended, or park the same nearer than three hundred feet to any location to which the city fire department has been called to extinguish a fire; provided, that the provisions of this section shall not apply to motor vehicles when used on official business nor when the motor vehicle was so parked and left standing prior to the outbreak of such fire.