<select name="shipping_zone" id="shipping_zone">
  <option value="0">- выберите область -</option>
  <?php foreach ($zones as $zone) { ?>
  <?php if(!empty($zone['id_area'])){ ?>
  <option value="<?php echo $zone['id_area'] ?>" ><?php echo $zone['name']; ?></option>
  <?php } ?>
  <?php } ?>
</select>

$("#shipping_zone").change(function () {
  var zone = parseInt($("#shipping_zone").val());
  console.log(zone);
  getCodeNovaposhtaCities(zone);
});

function getCodeNovaposhtaCities(zone) {
  var city = $("#shipping_city");
  $("#divregion").fadeIn("fast");
  city.attr("disabled", false);
  if(zone > 0){ }
  city.load( "order_change.tpl", {zone: zone}, );
}

public function getCodeNovaposhtaCities(){
  $zone = $_POST['zone'];
  $query = $this->db->query("SELECT * FROM `" . DB_PREFIX . "novaposhta_cities` WHERE Area ='". $zone. "'");
  //print_r($query);die;
  return $query->rows;
}