A newly discovered FaceTime bug lets people hear and even see those they are reaching out to on iPhones using the video calling software, sparking privacy fears.

The bug, initially outlined by Apple product and review website 9to5Mac.com, was reported by several media outlets.

A video posted at Twitter account @BmManski showing how simple it is to take advantage of the flaw and listen in on an iPhone being called using FaceTime logged more than a million views and was shared 10,000 times by early evening in California.

Apple iPhone users are being warned of a bug that allows eavesdropping on their devices through the FaceTime app

A newly discovered FaceTime bug lets people hear and even see those they are reaching out to on iPhones using the video calling software even if the other person doesn't pick up

Some Twitter users offered advice to disable the FaceTime application until a fix was in place.

An Apple statement quoted in US media said the iPhone maker was aware of this issue and has 'identified a fix that will be released in a software update later this week.'

When a phone number is dialed on FaceTime - the iPhone's internet-based voice and video calling feature - the caller can swipe up from the bottom of the screen and tap an option to add a person, according to video demonstrations.

If a caller enters their number as also being the added caller, a group call begins even though the person being called has not answered yet.

The issue is likely to cause embarrassment for the consumer tech giant that says it believes privacy is a 'fundamental human right'

The caller can then then eavesdrop on the person being called, and in some demonstrations peek through the front-facing camera. Declining a call breaks the connection.

'Disable FaceTime for now until Apple fixes,' Twitter co-founder and chief executive Jack Dorsey advised in a tweet.

Dorsey's message included a forwarded post by technologist Andy Baio.

'Want to see a really bad bug?' Baio asked in his post.

'You can FaceTime any iOS device running 12.1 and listen in remotely-WITHOUT THE OTHER PERSON ANSWERING THE CALL.'

The glitch is reported to affect iPhones using iOS 12.1 or later

Ironically, news of the problem broke on Monday, which was Data Privacy Day – an initiative by tech firms to promote awareness of device security.

That day, Apple chief Mr Cook tweeted: ‘We must keep fighting for the kind of world we want to live in. On this #DataPrivacyDay let us all insist on action and reform for vital privacy protections. The dangers are real and the consequences are too important.’

The blunder emerged as Apple was poised to release its quarterly results last night. Earlier this month, Mr Cook admitted that the company was struggling to sell iPhones in some countries, with many blaming the slowdown on price increases.

Rob Baillie, from the website Compare My Mobile, said the FaceTime glitch could have ‘serious repercussions’ for Apple.

He added: ‘They have been working really hard to maintain their market share. Privacy is a hot topic at the moment – we’ve seen thousands voting with their feet away from apps like Facebook, for losing their trust.’

Apple did not immediately respond to requests for comment.