A chilling video that shows a surfer in the midst of an attack by a large shark has been leaked from a desktop computer inside a NSW Police station, sparking an investigation.

The eight-second video appears to have been filmed using a hand-held device from inside the police station, and showed the attack playing on a computer screen.

In the footage a figure in a wetsuit can be seen as they frantically attempt to paddle on their surfboard away from a large dorsal fin and tail in the ocean, before they were pulled underwater.

The identity of the person attacked in the video is not known, and it is unclear whether they survived. 

The video started circulated online amid rumours it showed the moment budding surf star Kai McKenzie survived a shark attack on North Shore Beach in Port Macquarie on Tuesday.

His leg later washed up on the shore and surgeons scrambled to try and reattach it.

But the leaked footage does not appear to fit the description of that attack.   

NSW Ambulance worker Kirrin Mowbray told reporters Mr McKenzie fought the shark off before he caught a wave back to shore.

The clip, though short, does not show the surfer fighting back and no waves can be seen approaching behind him as the shark attacked.

The video was filmed from a screen that appears to be inside a NSW Police facility and shows a surfer paddling before a huge dorsal fin and tail appear in the water and drag them under 

Ms Mowbray also said there were no witnesses to that attack.

‘The only person that saw the shark was the young man himself,’ she said. 

In the leaked video, above the computer screen a poster is shown that reads ‘respect, pride, trust’ next to blue and white squares, which is identical to the NSW Police logo.

The exact same slogan and logo features on NSW Police merchandise, including lanyards and keep cups.

A used lunch container could be seen in front of the desktop screen on which the video was played.

NSW Police confirmed it is investigating how the video was leaked and posted online.

‘NSW Police are aware of a video circulating online and have commenced an investigation into how the video came to be released,’ a spokesperson told Daily Mail Australia.

‘The NSW Police Force does not tolerate this kind of conduct and will take appropriate action pending the outcome of the investigation.’ 

The video was shared online as the attack on Kai McKenzie, 23 (pictured) who suffered serious leg injuries at North Shore Beach in Port Macquarie, around 11am on Tuesday

He survived and was rushed John Hunter Hospital in Newcastle. The details of the leaked video do not appear to match the description of Mr McKenzie’s attack

The leak comes just days after Mr McKenzie’s was mauled by a shark. 

One bystander – an off-duty police officer walking their dog on the beach – witnessed a bloodied Mr McKenzie emerge from the surf about 11am.

He used his dog’s lead as a tourniquet to stem the bleeding from the wounded areas.  

Police and paramedics arrived at the scene a short time later before Mr McKenzie was rushed to Port Macquarie Base Hospital in a critical, but stable condition.

His devastated loved ones rushed to his bedside and have made the bleak admission Mr McKenzie faces a ‘long road to recovery’ regardless of whether or not the limb can be reattached.

Mr McKenzie’s neighbour Lauren Mac confirmed the 23-year-old had undergone surgery, but would not clarify the nature of the operation.

‘This is all the family wants released at this time,’ she said.

‘Kai is currently in John Hunter Hospital where he has had surgery and is in a stable condition,’ she wrote.

‘His mum and dad told me it’s going to be a long road to recovery regardless of the outcome.’

Mr McKenzie’s surfboard is pictured following the horrific shark attack at North Shore Beach in Port Macquarie on Tuesday morning

Mr McKenzie (pictured) is understood to have arrived at the isolated beach with a friend after he caught a ferry 

A  GoFundMe made by Ms Mac has so far raised over $130,000 for the young surfer.

He had only recently returned to the water after fracturing his neck.

‘So happy to be back surfing after having a fractured neck,’ Mr McKenzie posted on Instagram in January. 

He’s been described a ‘legendary fella’ and accomplished surfer, sponsored by well-known brands.

There have been five fatal shark attacks of surfers in NSW in the last 20 years and a smaller number of recorded non-fatal attacks.