Pop singer Justin Bieber announced in an Instagram post on Friday that he has Ramsay Hunt syndrome, a rare condition which is causing him partial facial paralysis.

The 28-year-old also said he would cancel his upcoming tour dates as he is "physically, obviously not capable of doing them".

"As you can see, this eye is not blinking, I can't smile on this side of my face, this nostril will not move," Mr Bieber explained in the Instagram video.

According to National Library of Medicine of the United States government, the Ramsay Hunt syndrome neurological condition caused by varicella-zoster virus that affects the nerves involved in facial movements. It is also known as herpes zoster oticus.

Varicella-zoster is the same virus that causes chickenpox in children and shingles in adults. When the nerves are inflamed, they lose their ability to function properly, which can cause facial palsy or paralysis.

The signs and symptoms of Ramsey Hunt syndrome can include pain, vertigo, hearing loss, sensitivity to sound, tinnitus (a chronic ringing in the ears), and loss of taste, as per a Morbidity and Mortality Report published by Centers for Disease Control (CDC) and Prevention.

The disease progresses rapidly and fully manifests itself in two to three days. While initially the patient may complain of difficulty in closing eye and facial weakness, it can lead to permanent weakness and long-term complications if not treated quickly.

The most common treatments for Ramsay Hunt syndrome are medications that treat the virus infection. There are some cases where patients have been given steroids too.