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 andsaddened" by the plight of those he spoke to.
He was especially moved by the tale of the 18-year-old woman who was raped.
She said she and a friend bribed a police officer to allow them to cross the border illegally last year and then met a taxi driver who promised her a job.
On her first night, the taxi driver took the woman, who was five months pregnant at the time, to a house to stay. A friend of the driver raped her there. "I screamed, no one heard me," the young woman said, crying as a watery-eyed Damon swallowed hard.
Aid agencies have expressed concern about an increase in sexual violence against women crossing over from Zimbabwe as well as a rise in the number of unaccompanied children making the journey.
Many must cross the crocodile-infested Limpopo River and enter South Africa through holes in the fence along the poorly patrolled border, often paying exorbitant fees to unscrupulous guides.
In one camp visited by Damon, about 5,000 Zimbabweans are camped on a sandy patch strewn with rubbish and personal belongings. Some have built makeshift structures out of plastic, and others sleep on pieces of cardboard. There are about a dozen toilets and only a few taps.
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.