A British teenager who fought to stay alive despite developing a brain tumour as a toddler shared his story on his 16th birthday in a video that has gone viral and prompted outpourings of others' struggles with illness.

Lewis Hine, from England's south Portsmouth city, posted a 1min 42sec video on Friday (March 17).

"Today is my 16th birthday," he wrote on Facebook. "Please help me celebrate by watching and sharing my video to raise awareness."

In the video, Lewis wrote that he was diagnosed with a brain tumour at 17 months old and "it changed my life forever".

He had more than 13 brain surgeries to stay alive, and shared raw photos of himself in hospital.

The teenager also has drug-resistant epilepsy and hydrocephalus, or water on the brain, where cerebrospinal fluid builds up in the brain.

Lewis has seizures on most days, and his life "is a challenge", but "one I'm willing to accept".

"People say I'm disabled as if it's a bad thing," he wrote. "But I say I'm lucky. I know what my challenges are. I never take anything for granted."

The video, which has been received more than 5.8 million views, 32,000 likes and 160,000 shares, drew plenty of birthday wishes from netizens.

Many also came forward to share their own struggles.

Janet Croker wrote: "My son died of a brain tumour 13 years ago. Well done Lewis for being so positive and helping others. I admire you, happy birthday."

Ilana Nires called his story an inspiration.

"I just showed it to my 13-year-old daughter who has become disabled due to a chronic illness," she wrote. Her daughter has been bed-bound for more than a year and suffers with several symptoms including nausea, perpetual migraines and full body pain.

"My daughter and I think you are absolutely incredible to overcome the obstacles that have been put in front of you," wrote Ms Nires.

Chelsea Rose shared that she has Williams Syndrome, a development disorder characterised by intellectual disability among other features.

"I have heart problems I would love to be your new friend," she wrote.

And making friends is a huge part of Lewis' life - he has started a project called Friend Finder that brings together children who do not manage to go to school regularly.

On his website, Lewis writes that he knows his condition cannot be cured, but he is not letting anything stop him from helping other children who experience the same thing as he does.

"I truly believe that having a friend is one of the essential things in life that everyone needs to help your physical and mental wellbeing. It's important to talk, to smile and laugh."

Friend Finder has helped more than 200 children make friends, according to Lewis' website.