In a strange medical case, a 15-year-old boy has puzzled doctors in America because he cries tears of real blood.

Calvino Inman of Rockwood, Tennessee, says his friends have called him "possessed."

The tears are uncontrollable and can last anywhere from 15 minutes up to an hour.

"I feel it coming up, like a tear, sometimes it will burn," the Daily Telegraph quoted him as saying.

The doctors have been unable to diagnose the condition until now but one theory claims he has haemolacria - literally meaning "bloody tears".

His mother Tammy said: "I just truly want somebody to say they can help us."