US pop star Lady Gaga has revealed she suffers from post-traumatic stress disorder since being raped at the age of 19.

"I suffer from a mental illness – I suffer from PTSD," she told the Today Show on a visit to a homeless shelter for young gay people in New York.

"I've never told anyone that before," the star, now 30, added.

Lady Gaga revealed in a radio interview two years ago that she was raped as a teenager.

"The kindness that's been shown to me, by doctors as well as my family and my friends, it's really saved my life," the singer said, after bringing presents to the astonished teenagers at the centre.

"Meditation helps me to calm down," she said, adding that she was struggling with her mental illness "every day".

Lady Gaga later tweeted: "Today I shared one my deepest secrets w/ the world. Secrets keep you sick w/ shame."

A tearful young person from the centre she visited said: "Lady Gaga's act of kindness today was a reminder that love still exists – and that there's still some for me."

On social media, her fans opened up with their own experiences in response.

"I remember how your music and your spirit got me through really hard times," one user tweeted back to the singer. "Now I'm 1723 days self-harm free."

"I have something to tell you. I also suffer from PTSD. This is the first time I say it too. I love you and I admire you so much," another replied.