"It's a very stressful thing because once they're down they can't get up; you have to get their harnesses off them as quickly as possible," he said.

"They were thrashing around while they were down. Once I calmed them down, they realised that they couldn't do anything and then they got back up when the harnesses were off."

The fall left one of horses with minor grazes on its hind legs, he said.

"I've been over there this morning to give them a bath. She's walking around perfectly," he said.

Kristin Leigh, campaign manager at Melbourne Against Horse-Drawn Carriages, said the group had been sent videos of blood marks along nearby ram tracks.

She said that even if Mr Hunter's account was correct, it still represented the risks of using horses to pull carriages in an urban environment.

"It's certainly not the first time it's happened, and if the authorities don't act it won't be the last," she said.

She said the group was seeking to have VicRoads change the definition of a vehicle to no longer include horse-drawn carriages.

"They continuously break road safety laws; we get messages on a daily basis," she said.

Last year, the City of Melbourne said it would stop granting permits to horse-drawn vehicles to park or offer rides on Swanston Street because of safety risks.

Mr Hunter said the horse falling over was a "freak accident" that had happened only once before in his time in the industry.

He said activists trying to get the industry banned had "nothing better to do".

"These horses are our bread and butter, so of course we look after them," he said.

"It's absolutely ludicrous. All the other operators, the horses are treated like gold. You can't take a horse into the city if they're not looking right."