The planning director shall be responsible for preparing the zoning ordinance and for submitting it to the city planning commission for its consideration and action. The commission shall review the proposed zoning ordinance and, after holding at least one public hearing on each proposed action, shall approve or reject it in whole or in part and with or without modifications. When approved by the commission, the proposed ordinance shall be submitted to the council for its consideration, and the zoning ordinance shall become effective when adopted by the council. The city council of such primary city may amend, supplement, or otherwise modify the zoning ordinance. Any such proposed amendment, supplement or modification shall first be submitted to the planning commission for its recommendations and report. The planning commission shall hold at least one public hearing with relation thereto, before submitting its recommendations and report. After the recommendations and report of the planning commission have been filed, the city council shall, before enacting any proposed amendment, supplement or modification, hold a public hearing in relation thereto. Notice of the time and place of hearings above referred to shall be given by publication thereof in a paper of general circulation in the city at least one time at least five days before the date of hearing. Notice with reference to proposed amendments, supplements or modifications of the zoning ordinance shall also be posted in a conspicuous place on or near the property upon which the action is pending. Such notice shall be easily visible from the street, and shall be posted at least five days before the hearing.