Internet tycoon Kim Dotcom will launch a new file-sharing site at his Auckland mansion on Sunday, exactly a year after armed police arrested him at the same venue in the world's largest online piracy case.

Dotcom's new venture, mega.co.nz, aims to recreate the success of his Megaupload empire, which boasted 50 million daily visitors and accounted for four percent of all Internet traffic before it was shut down after the police raid.

The 38-year-old, who changed his name from Kim Schmitz, remains free on bail in New Zealand as US authorities seek his extradition on a range of charges including money laundering, racketeering and copyright theft.

They allege Megaupload sites netted more than $175 million in criminal proceeds and cost copyright owners more than $500 million by offering pirated copies of movies, TV shows, music and other content.

Dotcom denies any wrongdoing and the charges, which carry jail terms of up to 20 years, have not discouraged him from launching the new Mega service, which he has enthusiastically promoted on Twitter in recent weeks.

"I think you will be very happy with the new #Mega," he tweeted Friday. "It's like time travel. We'll take you to the future!!!"

The tech entrepreneur has promised an "epic" launch for the new site and even impersonated Willy Wonka to promote it at an Auckland shop on Thursday, handing out tubs of ice cream with golden tickets to the event hidden in them.

Details of the planned service are scarce, but the site promises to use state-of-the-art encryption methods that mean only users, not the site's administrators, know what they are uploading.

That would theoretically stop authorities from accusing administrators of knowingly aiding online piracy, the central allegation facing Dotcom.

Dotcom has said Mega will offer users 50GB of free storage, significantly more than similar sites such as Dropbox and Google Drive, but most details remain under wraps until they are unveiled Sunday at the Dotcom Mansion.

The German national was preparing for his birthday party at the lavish Auckland property in January last year when armed police staged a dawn raid, tracking him down in a hidden panic room running off his bedroom.

Officers seized more than a dozen luxury cars, including a 1959 pink Cadillac, along with valuable artworks and a sawn-off shotgun, while Dotcom's bank accounts were frozen and he spent more than a month in jail.

Eventually freed on bail, his legal team have enjoyed a number of successes challenging the prosecution case, including a ruling that the police raid was illegal and a government admission that Dotcom was illegally spied upon before his arrest.

The extradition hearing is due to be heard in August.