Two inquiries into the existence of a black panther concluded there was 'most likely' a big cat roaming in western Sydney but they were never released publicly - sparking claims of a cover up.

Hundreds of sightings of a big cat lurking in the Blue Mountains have been made and rumours of its existence have been circulating for more than a century, but there has never been any undisputed evidence.

A report commissioned by the Department of Primary Industries in 1999 said there was 'most likely' a 'large feline predator' in New South Wales - 'difficult as it seems to accept'.

Two enquiries into the existence of a black panther concluded there was 'most likely' a big cat roaming in western Sydney

Report writer Johannes Bauer said heading to the site of the alleged sightings was 'really quite staggering'

The report was written by wildlife ecologist Johannes Bauer, who told the ABC the DPI's interest in the panther was related to liability.

'They were worried something might happen and because they hadn;t taken it serious that someone might take them to court,' he said.

He said heading to the site of the alleged sightings was 'really quite staggering'.

A second report from DPI concluded that the 'free-ranging, exotic, large cats in New South Wales... seems more likely than not on available evidence'.

A secret report written in 2008 has led those who believe there is a panther roaming in NSW to make claims of a cover up.

'There is no scientific evidence found during this review that conclusively proves the presence of free ranging exotic large cats in NSW, but a presence cannot be discounted, and it seems more likely than not on available evidence that such animals do exist in NSW,' the report said.

It was not publicly released, and a follow up report made public in 2009 seemed to contradict earlier findings.

'Whilst information has been provided, there is still nothing to conclusively say that a large black cat exists,' it said.

Hundreds of sightings of a big cat lurking in the Blue Mountains have been made and rumours of its existence have been circulating for more than a century

Mike Williams, author of Australia Big Cats, questioned why there were two reports carried out by DPI in such a short timeframe.

A final report in 2013 bluntly stated there were no large cats in the wild in NSW.

'The sightings and other evidence presented, mostly from the Hawkesbury region, are at best prima facie evidence.'

Steven Musier claimed to have seen a giant cat roaming near Cox's River in the Blue Mountains on the weekend.

He filmed the feline and said it was 'definitely not a feral cat' and 'as wide as the bonnet on my ute'.

'We got out and started filming it, it wasn't a domestic cat gone feral, it was much bigger than that, probably five times that size.'