Naomi Watts has confessed that making tsunami film The Impossible was the "most physically demanding thing I've ever done".
The 44-year-old actress stars with Ewan McGregor and rising star Tom Holland in the true story of Maria Belon and her family, who were holidaying in Thailand in 2004 when the Indian Ocean tsunami struck.
The stars of the film joined Ms Belon at a charity screening at the BFI Imax cinema in London, held in aid of Indian Ocean Disaster Relief, which helps families affected by the disaster.
Naomi, a mother of two, praised Ms Belon's determination to stay alive and save her sons.
She said: "Every mother wakes up with fear of her children's safety, so I just cannot imagine how she dealt with it. That was the thing that struck me - how courageous and heroic she was.
"I consider myself one of those people who are just hopeless in a crisis but she said she never felt more connected to her centre and every decision she made felt like the correct one.
"You kind of crave to have that. But it's hard."
Directed by Spanish filmmaker Juan Antonio Bayona - director of critically acclaimed horror film The Orphanage - The Impossible follows Ms Belon, her husband and her three young sons in their fight for survival.
Ms Belon insisted it is a story of hope.
"You can never give up if you have life," she said. "You can never give up. That's how I got from the tsunami. If we are alive, we have hope."