Unable to read Javascript responseXML from PHP

I have a database of shipping zones that I want to access through an AJAX request using PHP.

If I change to xml.responseTEXT I am able to read the last entry and appropriately add it as an option to my select menu.

I tried encoding my PHP output into simpleXML() and was able to use .innerHTML=value to print the result to my webpage, but unable to parse the content to be used to create options for my select menu.

Here is my PHP to generate XML `

mysqli_select_db($con,"ajax_demo");
$sql="SELECT * FROM `shipping_zones` WHERE zone_type = 'Province' and     parent_zone = '$country_id' ORDER BY zone";
$result = mysqli_query($con,$sql);

echo "<?xml version=\"1.0\" ?>
    <shipping_zones>";
while($row = mysqli_fetch_array($result)) {
    echo "<province>
            <zoneid>" . $row['id'] . "</zoneid>
            <zone>" . $row['zone'] . "</zone>
        </province>";
}
echo "</shipping_zones>";

mysqli_close($con);

?> `

Here is my XML output from PHP <?xml version="1.0" ?> <shipping_zones><province> <zoneid>597</zoneid> <zone>Alberta</zone> </province><province> <zoneid>595</zoneid> <zone>British Columbia</zone> </province><province> <zoneid>605</zoneid> <zone>Labrador</zone> </province><province> <zoneid>594</zoneid> <zone>Manitoba</zone> </province><province> <zoneid>606</zoneid> <zone>New Brunswick</zone> </province><province> <zoneid>604</zoneid> <zone>New Foundland</zone> </province><province> <zoneid>600</zoneid> <zone>Northwest Territory</zone> </province><province> <zoneid>603</zoneid> <zone>Nova Scotia</zone> </province><province> <zoneid>598</zoneid> <zone>Nunavut</zone> </province><province> <zoneid>596</zoneid> <zone>Ontario</zone> </province><province> <zoneid>607</zoneid> <zone>Prince Edward Island</zone> </province><province> <zoneid>601</zoneid> <zone>Quebec</zone> </province><province> <zoneid>602</zoneid> <zone>Saskatchewan</zone> </province></shipping_zones>

Here is my Javascript `

function changeCountry(){
                var e = document.getElementById(\"country_id\");
                var country_id = e.options[e.selectedIndex].value;
                if(country_id == 1){
                    // Display states
                        document.getElementById('display_province').style.display = \"none\";
                    document.getElementById('display_state').style.display =     \"\";
                        document.getElementById('display_state').style.visibility = \"visible\";
                }
                else{
                    // Display Province
                    document.getElementById('display_state').style.display =     \"none\";
                        document.getElementById('display_province').style.display = \"\";
                    document.getElementById('display_province').style.visibility = \"visible\";
                    // Remove current selection list 


                    // Get Provinces for country_id
                    var xmlhttp = new XMLHttpRequest();
                    // Include fix for IE6 and IE5
                    if (window.XMLHttpRequest) {
                        // code for IE7+, Firefox, Chrome, Opera, Safari
                        xmlhttp = new XMLHttpRequest();
                    } else {
                        // code for IE6, IE5
                        xmlhttp = new ActiveXObject(\"Microsoft.XMLHTTP\");
                    }
                    xmlhttp.onreadystatechange = function() {
                        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
                            var xmlDoc = xmlhttp.responseXML;
                            // get each property 
                            // Last known execution
                            var x=xmlDoc.getElementsByTagName(\"province\");
                            for (i=0;i<x.length;i++)
                            { 
                                var e = document.getElementById(\"province_id\");
                                var opt = document.createElement('option');
                                opt.value = x[i].getElementsByTagName('zoneid')[0];
                                opt.innerHTML = x[i].getElementsByTagName('zone')[0];
                                e.appendChild(opt);
                            }
                        }
                    }
                    xmlhttp.open(\"GET\",\"get_provinces.php?country_id=\"+country_id,true);
                    xmlhttp.setRequestHeader(\"Content-type\", \"text/xml\");
                    xmlhttp.send();
                }
            }

`

Is my error in encoding the PHP output into an object? Is my error in parsing the responseXML?

Thanks