ACTOR Ewan McGregor has revealed he broke down in tears at the thought of losing his children while shooting a film about the 2004 Boxing Day tsunami.

The father-of-four said he was overwhelmed with emotion during filming of The Impossible at one of the areas in Thailand affected by the tragedy.

More than 230,000 people died in 14 countries after an earthquake unleashed a sub-sea tidal wave.

The film is based on the true story of a Spanish couple and their two young boys who survived the catastrophe.

McGregor said: "I was just crying my eyes out, and that's why I think it's valid to make the film because it is all about the human spirit and a unique look at what makes us tick."

The 41-year-old, who is an Ambassador for Unicef, added that at first he did not want to make the film, which co-stars Naomi Watts.

He said: "I was very wary. Many, many people lost their lives, and the idea of making a movie about it didn't sit very well on my shoulders.

"It was a huge undertaking to make that film. Director Juan Antonio Bayona wanted to use real water, so there was six or seven weeks in a huge filming tank in Alicante, Spain, which was very difficult.

"Then we shot our story in Thailand. Juan went off and shot like a third scale model of the actual wave hitting the hotel our characters were staying in."