Hato Paparoa was once one of the faces of Child Cancer, but this year signed autographs until his arm hurt at the Berlin film festival.

The 13-year-old's film debut, The Strength of Water, in which he plays Kimi from the Hokianga - a character similar to himself - hits New Zealand cinemas this week.

Hato's journey from the children's cancer ward to the paparazzi-trimmed red carpet is a true tale of overcoming the odds.

At 5 years old he was diagnosed with fourth-stage Hodgkin's Disease and was given less than a year to live.

His parents, who were heavily involved in their other five children's schooling, sports, their community, kapa haka and were both working, dropped everything to move to Auckland's Starship children's hospital where Hato received 24-hour care, chemotherapy and white-cell transplants.

After a two-year battle, he was given the nod to return home to Motuti in the Hokianga.

Over the next two years he regained his strength and started school while still making regular trips to Starship for monitoring.

But while acting as a gofer for his father at a Hokianga beach race soon after he had regained his health, he was spotted by the Strength of Water's casting director Suzanne McAleer.

She knew right away that the energetic 10-year-old was the film's Kimi, but it was not as simple as signing him up on the spot as the family moved to Hawkes Bay before the auditions.

More than 1000 children auditioned but she could not shake the image of Hato.

Finally she tracked the family down and asked Hato to attend an audition in Auckland.

After what his father said seemed like a five-minute interview, Hato was cast as Kimi.

Ms McAleer found Melanie Mayall-Nahi, who played Kimi's sister Melody, in Auckland - she turned out to be one of Hato's cousins.

Hato found he easily slipped into the character of Kimi.

Both are from the Hokianga Harbour, have a lot of sisters they are close to, and love food, he said.

"It was pretty easy to get into the emotions because I was like Kimi, Kimi was like me, we had both done the same things."

Despite the long hours, and being put off hot dogs for life after eating 54 for one scene which ended up being cut from the film, Hato hopes to continue acting.

He said it was pretty embarrassing watching himself on screen, especially scenes that involved swearing - which is forbidden in his Catholic family.

But he loved the buzz of the opening in Berlin, and was more than happy to sign autographs, though he said: "My arm got a bit sore".

The Strength of Water is a German-New Zealand co-production, directed by New Zealander Armagan Ballantyne and written by Briar Grace-Smith. It has screened at festivals around the world including Cannes, Seattle and Shanghai.

A New Zealand preview will be held at a fundraiser for the Child Cancer Foundation tomorrow.