"He was swearing, and saying, 'Get out of here, go back to where you came from'."
After the driver heard the tirade she turned the engine off, stood up and walked down the bus to confront the man.
"She said to him, 'You need to leave'," Mueller said.
"He asked her why, and she said, Because you are saying racist, abusive things'."
The man became angry and began swearing at the driver, and punched her in the arm, Mueller said.
She and another passenger quickly stood up to intervene.
The man eventually got off the bus.
"It all happened really fast, but we thought the driver did a really good job. It was quite frightening and we were scared it could escalate further."
Auckland Transport said the driver, employed by their operator NZ Bus, confirmed the incident took place, but did not want to draw attention to herself.
A spokeswoman said they commended the driver for her actions.
"Auckland Transport and our operators do not tolerate anyone that makes our passengers or staff feel unsafe, especially when that negative behaviour is targeted at who they are.
"Several of our operators have specific training to deal with this negative behaviour and we commend the driver for intervening in what can be a very frightening experience."
Mueller, who is originally from Brazil, said she wanted to share the story about the driver to encourage more people to stand up to racism.
"It was a little disappointing more people did not stand up to what was happening.
"But it is moments like these, with the driver, that need to be shared to show that people in Auckland really are against racism."
Mueller said police had been contacted about the incident.
The Herald has contacted police for comment.
