When your visa expires while you are still in New Zealand, you become an "overstayer". If you are wanting to reinstate your visa status by lodging a new immigration application, you must do so under s61 of the Immigration Act 2009. It must be noted, however, that Immigration New Zealand is under no obligation to accept the application for processing, give consideration to it, or give an explanation if it is refused or declined.
If you have run out of your visa, it would be probable that any subsequent s61 application that you lodge is likely to fail, unless you can show to Immigration New Zealand that there are compelling reasons as to why you should be granted a visa.
The fact that you have overstayed does not, however, mean that it is all doom and gloom. We have helped numerous clients set things right with Immigration New Zealand who received favourable outcomes on their s61 applications. Talk to us and ensure the chances of getting a new visa approved are maximised.