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The mystery of the missing Malaysia Airlines flight is getting deeper and deeper.

It has emerged that phones taken on board flight MH370 are still ringing FOUR DAYS after the plane's disappearance.

Reports suggest as many as 19 families have managed to call phones of their missing loved ones, while the airline itself has got through to some of the missing crew's handsets.

According to Chinese media, the 19 families have signed a joint statement confirming they made calls which connected to the missing passengers but without an answer.

In addition a Malaysia Airlines official confirmed that they too had tried to get in touch with cellphones of missing crew members, but again without a response.

And even more bizarrely, some social media sites have shown missing passengers as still being 'online'.

One man said that his missing brother's QQ profile - a Chinese social networking site - was still logged in.

But frustratingly for all the heartbroken families all messages or calls are yet to be reciprocated.

This isn't the first time that the phones of those people missing were able to be 'reached'.

(Image: Reuters)

On Sunday, a family of a passenger successfully rang his phone live on television, but received no answer.

The fresh news about the phantom phones and social media presence has given those waiting for any news renewed hope.

But it may all not be as it seems, with phone networks and carriers perhaps to blame.

While you would expect that when you hear a ring tone the phone is on and in working order that may not actually be the case - according to one expert.

"That does not mean the phone you are calling is ringing yet," wireless analyst Jeff Kagan told NBC News.

"The network is searching for the phone. First based on where it last was, then it expands. Then if the network can't find the phone, the call terminates."

Apparently even if the phone in question is in airplane mode - or is off or terminally broken - it may still ring on the caller's end, despite there technically being no chance of it being connected.

The search for the missing flight is moving into its fourth day with the search parameters being expanded further.

The flight is presumed to have crashed off the Vietnamese coast on Saturday, after losing contact with air traffic controllers off the eastern Malaysia coast.

Fears terrorists were to blame grew as it emerged two passengers were using stolen passports.

But it has now come to light that one of the men, 19-year-old Iranian Pouria Nour Mohammed Mehrdad, was looking for asylum in Germany and had no terror links.

Follow all the latest breaking news from the search for the missing plane with our rolling live blog.