Melbourne commuters were left shocked after a man launched into a racist and violent rant on a city bus when a Frenchwoman was abused for singing in her native tongue.

Video footage of the incident, taken by passenger Mike Nayna, shows three people - including a man pushing a pram - threatening the woman.

"Speak English or die," a middle-aged man shouted at the woman, who was sitting at the back of the bus.

He later continued: "Everyone on the bus wants to kill ya! You're gonna have to get off eventually b***h. You worked that out yet?"

Nayna said a woman, believed to be the partner of a man with a pram, heckled the French woman, to which she replied: "Just go; you can go now."

He said that prompted the man with the pram to start threatening, her saying he would "cut her with a boxcutter".

When the man pushing the pram left the bus, he smashed the window closest to the woman from the outside.

Nayna said it was worrying how the abusers fed off each other and became a mob.

"It didn't make any sense. There was no logic," he said.

"It was just weird mob mentality. They were feeding off each other and breaking off into rants and encouraging each other over some racist stuff - it was like a bonding session."

Nayna, who has light-brown skin, said at one point he tried to stop the fracas but he was also abused with a rant about how black people should sit at the back of the bus.

Another passenger offered one of the abusers his fishing knife and gave him a beer.

"Then he went off on a tangent about filleting people and saying 'They're just scared c**** at the back of the bus."

Nayna said police had contacted him about the footage.

He said he had uploaded the footage to shame those involved and who were featured in the video into realising what they had done.

- © Fairfax NZ News