Avoid rebuilding with msbuild /t:Package?

I wish to create a zip web site package for later msdeploy. I used msbuild command line tool

msbuild xxxx.csproj /p:PackageLocation=outputDir\xxxx.zip /t:Package 

msbuild did pack the website, but it also rebuild the website before packing it. The problem is that the website was already built (it contains pages and all the dlls already) before I call msbuild /t:Package.

Is there a way to avoid rebuilding with msbuild /t:Package ?