How to Implement Loading in Asp.net

<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>

  <asp:Timer runat="server" ID="timer1" Interval="300000" OnTick="UpdateTimer_Tick">
    </asp:Timer>

//On c# Hand

protected void UpdateTimer_Tick(object sender, EventArgs e)

{
     BtnSearch_OnClick(sender, e);
     lblLastUpdate.Text = System.DateTime.Now.ToString("dd-MMM-yyyy hh:mm:ss");

}

<asp:UpdatePanel ID="UP1" runat="server">
    <ContentTemplate>

        --------------------CONTENT HERE----------------------

    </ContentTemplate>
 </asp:UpdatePanel>

 <asp:UpdateProgress AssociatedUpdatePanelID="UP1" ID="updateProgress" runat="server">
        <ProgressTemplate>
            <div id="processMessage" style="position: absolute; top: 45%; left: 45%; padding: 10px;
                width: 22%; z-index: 1001; background-color: yellow; font-family: Arial; font-weight: normal;
                font-size: 10pt; border: thin solid #9CAAC1; height: 65px; text-align: center;">
                Please wait while the document is<br />
                being processed.<br />
            </div>
        </ProgressTemplate>
    </asp:UpdateProgress>