Mapnik vector tiles rendering ignores zoom level

I'm trying to render vector tiles using node-mapnik mapnik.VectorTile feature:

var map = new mapnik.Map(256, 256);
var mercator = new sphericalmercator({size: 256});
map.loadSync("../openstreetmap-carto/openstreetmap-carto.xml");
var bbox = mercator.bbox(0,0,0, false, "900913");
map.zoomToBox(bbox);
var vtile = new mapnik.VectorTile(0, 0, 0);
map.render(vtile,{},function(err,vtile) {fs.writeFileSync('0.vector.pbf', vtile.getData());});

The problem is that this code is trying to render the whole world in all small details (as for a big zoom level) into one big tile file. It ignores zoom rules that on the zoom level 0 it should only show country borders, not all map features. When I'm trying to render the map into a png file the result is fine. The question is how can I set a preferred zoom level for the vector tile renderer?

Thank you.