Set 'collapsed' property to true for the north panel. When the north panel is collapsed, get the corresponding 'expandNorth' panel and close it. Finally call 'resize' method to resize the layout.
<div id="layout" class="easyui-layout" style="width:700px;height:350px;">
	<div style="height:150px" data-options="
			region:'north',
			collapsed:true,
			onCollapse:function(){
				setTimeout(function(){
					var p = $('#layout').layout('panel','expandNorth');
					p.panel('close')
					$('#layout').layout('resize')
				},0)
			}"></div>
	<div data-options="region:'center'"></div>
</div>