The Hollywood actor was visiting refugee centers in this border town as part of his work with Not On Our Watch, a human rights group he started with other celebrities such as Brad Pitt and George Clooney to draw attention to the world's suffering peoples.
"I have spoken to so many people who went through so much to get to this point. It is testament to the situation across the border in Zimbabwe," Damon told The Associated Press in an exclusive interview.
An estimated 3 million Zimbabweans have fled economic collapse and dire humanitarian conditions at home, and Damon said he was "shocked and saddened" by the plight of those he spoke to.
Damon, who patiently listened to heart-wrenching stories in the scorching heat, called the situation in Musina "untenable" and said "action has to be taken" by international and regional leaders.
Damon is in South Africa making a film directed by Clint Eastwood and starring Morgan Freeman as the country's first black president, Nelson Mandela. He said he hoped to use his "celebrity capital" to raise awareness about Zimbabwe, where a new unity government is calling for $2 billion in aid to help rebuild.
The film will be shot entirely on location in and around the cities of Cape Town and Johannesburg, South Africa, utilizing hundreds of local crewmembers, cast and extras.
In a joint statement, the film’s producers expressed their appreciation for the cooperation extended to them, saying, “We want to thank the people and the government of South Africa for their gracious hospitality and their cooperation. We are thrilled to be in their beautiful country and look forward to living and working here in the weeks ahead.”
Mr. Eastwood added: “We are honored to have the full support of the Nelson Mandela Foundation and South African Rugby as we set out to capture this unforgettable chapter of their shared legacy.”
In a radio interview on Wednesday morning, Damon said he had been inspired by Pienaar.
Pienaar is climbing Mount Kilimanjaro with fellow Bok Hennie le Roux and a few friends, and plans to descend in time to cycle the Tour on Sunday - all to raise funds for the charity Make a Difference (MAD).
Damon said he had been inspired to sign up for Sunday's race alongside Pienaar.
"I think I've got a little bit of 'mad' in me too!" confessed the movie star.