Director General of Health Ashley Bloomfield is reassuring New Zealanders their privacy will not be compromised by the Government's new Covid Tracer App.

It was made available on app stores overnight, but there are concerns many people will not download the app due to fears about sharing personal details with the Ministry of Health.

But Bloomfield says there are strict rules about how the data can be used.

"It has a function that allows them to scan QR codes at places they visit, then that data is only held on their phone and it's up to them to release it if they are then a contact."

The app, named NZ Covid Tracer, was originally due to launch today and it is unclear why it was released a day early.

Once signed in, users are able to scan QR codes at businesses, public buildings and other organisations to track where they have been for contract tracing purposes.

From there, people can see their "check-in" history.

Users can also register their details to the National Close Contact Service in order for them to be able to contact quickly if needed.

A feature coming soon to the app is a "daily self-isolation check-in" which help those who are by themselves to complete a daily health check-in in case they need help.

The app also links to other contact-tracing resources and also provides Covid-19 update notifications.

It also has a nice reminder at the bottom of the homepage, advising people to remember to wash their hands often with soap.

User's data is kept securely on their phones. It will be stored for 31 days and then automatically deleted, according to the app.

"By signing up to this app, you're helping keep yourself and your family safer and supporting New Zealand to stop the spread of Covid-19," Dr Bloomfield is seen quoted on the website linked to the app.

"This will ensure we can all return to doing the things we enjoy as soon as possible."

Jacinda Ardern announced last Wednesday the Government would be launching a "digital diary app" to aid physical contact tracing methods.

Ardern said it was simply a way of recording where you've been and didn't need significant sign-up to be effective.