A mysteriously large cat likened to a black panther has been filmed roaming the NSW countryside.

Steven Muiser spotted what looked like “a big black cat” prowling the Blue Mountains in NSW while he was in Kanimbla Valley.

“It was as wide as the bonnet of my ute,” he told Channel Nine on Tuesday.

The Blackheath man said the strange feline was 60 centimetres tall and about five times the size of a normal feral cat.

“We see feral cats all the time, and we could film them all day long and that was definitely not a feral cat.”

Mr Musier watched what he described as a “feral cat on steroids” walk “over the hill” for about 20 minutes.

“You just had to have been there to see it, it was huge. It had that big cat swagger.”

Professor Barry Brook, wildlife biologist from the University of Tasmania, said the sighted feline was mostly likely not a large panther.

It could have merely been a domestic cat but “the optical illusion gave it a sense of scale that it was much larger than in reality”, he told The New Daily.

If it was indeed a panther, the animal must have escaped captivity from a zoo or a circus as they are not native to Australia, Professor Brook said.

“A circus has become increasingly unlikely given that those sorts of animals aren’t really kept these days … and if it was a zoo we would know about it,” Professor Brook said.

“So unless it was something that was released decades ago and has established a breeding population, it stretches the bounds of credibility to imagine that it could be some descendant of some escaped animal.

“Then you would obviously need to have many of them or at least a pregnant female to have escaped and be able to perpetuate in secret a population of these large predatory cats.”