Well you would want to handle the world creation asynchronously.
If you meant that you want to create a world as an arena for mini-game for example, what you would want to do is to copy the "source" files (your main world) .
Here is an old post that will teach you how to do it.
Important thing to note is: If you are running Asynchronous task, some of the Bukkit Api won't work and could potentially cause errors.
