Prime Minister Scott Morrison says he is confident that the NSW Government "will get on top" of a new coronavirus testing regime which has led to thousands of cars queuing for hours at a southwest Sydney testing site just to be able to work.

Lines at the 24-hour testing hub at Fairfield showground have been growing overnight as essential workers rush to get tests so they can keep up with new NSW Health orders. 

The new orders require essential workers who live in the Fairfield region to get tested every three days and prove they have a negative result for work.

The testing lineup scene has been described as "chaos", with people waiting in cars for anywhere up to eight hours to get tested.