British actor Tom Hiddleston struggled to sleep during a charity trip to West Africa because he was "overwhelmed" by the sight of so many sick and malnourished children in hospital.

The Thor star travelled to Guinea in January (13) to visit communities which have been helped by the United Nations Children's Fund (Unicef) programs, and he admits a trip to a medical centre in the capital city of Conakry was an emotional experience.

In a piece for Harper's Bazaar magazine, he writes, "(During the visit) I was delighted, enlightened, and confused. I immediately got a real sense of one of the biggest challenges that children face in the country: hunger and malnutrition.

"We visited (the) National Institute of Child Health and Nutrition (Inse) in the Donka Hospital in Conakry... (And) I was simply overwhelmed by seeing so many small infants in such great need.

"One small ward... housed at least 20 children, some of whom had slim chances of survival... Most shocking to me was the speed and urgency of their breathing, asleep or awake, it was uniformly unsettled and uneven. When you see a child struggling so hard simply to breathe, it makes your heart hurt.

"It was tough to get to sleep that night, remembering the sight of those children, but I had come expecting the week to be a tough one, full of mixed emotions."

Summing up his trip, the actor adds, "Now that I am back to the hustle and bustle of London, I miss the warmth and people of West Africa... The week that I spent in Guinea was truly life changing."