A hacker has released test gameplay footage of upcoming video game Grand Theft Auto VI, in what has been described as one of the biggest leaks in video game history.
Labelled "early development footage" by developer Rockstar Games, the footage consists of more than 90 separate video clips showing animation tests, level layouts and full-blown gameplay demonstrations.
It also appears to confirm long-running rumours that the game, which is still in development, will feature the series' first playable female protagonist, with one of the longer leaked sequences depicting a woman holding up a diner.
The video clips were posted on Sunday to the GTAForums site by a user going by the name "teapotuberhacker", who claimed to have accessed internal Rockstar employee communications on the Slack messaging app.
A similar technique was recently used to access the internal communications of rideshare company Uber.
While the original post with the leaked footage has been removed by forum moderators, clips and screenshots have since been widely shared on social media.
Developer Rockstar Games confirmed the leak was genuine on Monday, posting a short statement to its social media accounts blaming a "network intrusion" by an unauthorised third party for the leak and promising to properly introduce players to the game when it is ready.
"At this time, we do not anticipate any disruption to our live game services nor any long-term effect on the development of our ongoing projects," the company said.
"We are extremely disappointed to have any details of our next game shared with you all in this way.
"Our work on the next Grand Theft Auto game will continue as planned and we remain as committed as ever to delivering an experience to you, our players, that truly exceeds your expectations."
'A nightmare for Rockstar Games'
US video game journalist Jason Schreier said the leaks were a "nightmare for Rockstar Games", and could affect the company's work on the project for an undetermined period of time.
"It may [also] lead management to limit work-from-home flexibility," Mr Schreier wrote on Twitter on Sunday.
The hacker also appeared to have access to the game's source code, the raw coding of the game as written by its developers.
If that code were to be made public, the company would likely have to devote significant resources to altering the game’s underlying structure, so as to reduce its vulnerability to possible exploits after the game’s release.
After the clips from the GTA VI leak went viral, the hacker posted another message saying they "woke up to 3000 Telegram DMs" and were now "looking to negotiate a deal" with Rockstar or its parent company, Take-Two.
GTA series is blockbuster entertainment
The Grand Theft Auto series is one of the most successful franchises in video game history, generating more than $US7.68 billion ($11.4 billion) in net revenue since 2013, when the series' latest major instalment was released.
It bills itself as a satire of the American dream, mixing crime- and gang-related gameplay with biting commentary on politics, corporate advertising and pop culture.
The games' open embrace of stereotypes and graphic depictions of violence and sexuality have also made them a magnet for controversy, with some major Australian retailers pulling GTA V from shelves in 2014 over concerns with its content.
Industry watchers currently expect GTA VI to have a release date of 2024 or 2025.
