<asp:ScriptManager ID="ScriptManager2" runat="server" />
<asp:UpdateProgress runat="server" ID="PageUpdateProgress">
<ProgressTemplate>
<asp:Image ID="Image1" AlternateText="Loading..." runat="server" />
</div>
</ProgressTemplate>
</asp:UpdateProgress>
<asp:UpdatePanel runat="server" ID="Panel">
<ContentTemplate>
<asp:Button runat="server" ID="Button1" OnClick="Button1_Click" Text="Display" />
</ContentTemplate>
</asp:UpdatePanel>
protected void Button1_Click(object sender, EventArgs e)
{
//display loading symbol for 3 sec
System.Threading.Thread.Sleep(3000);
}