NSW has recorded two new coronavirus cases overnight as over a million people download the new contact tracing app.

The optional COVIDSafe app launched last night to help states carry our efficient contact tracing.

The app uses Bluetooth to track and log close contacts with anyone else who has the app on.

Then, when someone contracts COVID-19, a warning message can be sent to those app-users so they can self-isolate and manage symptoms.

Australians are being encouraged to download the app with the federal government hoping for a 40 per cent uptake.

Premier Gladys Berejiklian says the tool is vital in the coronavirus fight.

“It is really important for our citizens to download the app,” she said.

Nine Radio’s tech expert Charlie Brown told Ray Hadley members of the public shouldn’t fear an invasion of privacy.

Data retention lasts only 21 days, and remains encrypted on the device unless the user opts to share it with the health department.

“The thing to remember with all of this, is that when you put it on your phone it doesn’t share anything.

“For example, Ray, I might never test positive for COVID-19 – in that case, I would delete the app at the end of all of this and the data will disappear off my phone, never to be seen by anybody.”

One of the app’s issues is incompatibility with older, cheaper smartphones.

The Department of Health has been contacted for comment.

Click PLAY below to hear the full explainer