The NHS Covid-19 App has been updated to fix alerts suggesting exposure to coronavirus that then disappear.

Users have said the notifications appeared on their phone, but then disappeared when they opened the app.

Many suggested the alerts were worrying and caused confusion over whether they had been exposed and needed to isolate or get a test.

But the messages were caused by default privacy notifications from Apple and Google, which provide the technology the app is built on.

The messages are designed to alert users that their app is sharing anonymous contact-tracing information with another app.

The messages will still appear following the update, but will now be followed by a message from the government telling users to ignore them.

A Department of Health and Social Care (DHSC) spokesperson confirmed app users “only need to self-isolate if they get a notification directly from the app advising them to do so”.

Official notifications from the app won’t disappear when you click on them and will provide appropriate advice within the app, DHSC confirmed. Important messages will always be visible within the app, even if a user misses the original notification.

An update on the App Store said the app had been fixed for “better notification for potential exposures”.

The app, launched in England and Wales on 24 September, uses Bluetooth to track time and distances between smartphone devices. Exposure notifications are shared between devices that have recently been in contact.

If a user comes into close contact with someone who later tests positive for the virus and needs to self-isolate, the app will send a message stating it has “detected that you have been in contact with someone who has coronavirus. Please stay at home and self-isolate to keep yourself and others safe”.

The technology behind the app is based on Apple and Google’s decentralised model, which has consistently been hailed more privacy-centric as it only sends exposure notification alerts between devices.

The system generates a random ID for an individual’s device, which can be exchanged between devices via Bluetooth, not GPS. These unique random IDs regenerate frequently to add an extra layer of security and preserve anonymity.