Megaupload founder Kim Dotcom talks to members of the media as he leaves the High Court in Auckland. File picture: Reuters

Wellington - The legal saga over the extradition of former internet mogul Kim Dotcom was set for a final showdown at a five-day appeal hearing that began in New Zealand's Supreme Court on Monday.

In December 2015 Auckland's District Court ruled that Dotcom, founder of the file-sharing service Megaupload, and his associates were eligible for extradition to the United States to face criminal charges including conspiracy to commit racketeering, copyright infringement, money laundering and wire fraud.

The decision was upheld by the country's High Court in February 2017 and the Court of Appeal in June 2018.

If the Supreme Court should find that Dotcom as well as associates Mathias Ortmann, Finn Batato and Bram van der Kolk are eligible for extradition, the final decision still lies with New Zealand's Justice Minister.

Dotcom wrote on Twitter on Monday, "in 2005 I created a website that allowed people to upload files to the cloud.

"At the time only small files could be attached to emails. Megaupload allowed users to email a link to a file. That's it.

"In 2019 the NZ Supreme Court decides if I should be extradited for this 'crime'," he added. 

The tech mogul, born as Kim Schmitz in Kiel in Germany, has been resident in New Zealand since 2010.

His website Megaupload made millions from advertising and premium subscriptions. At its peak, Megaupload was the 13th most popular site on the internet and accounted for 4 per cent of all online traffic.

Dotcom and three of his former colleagues could face decades in jail if extradited to the US and found guilty.

The hearing is expected to last until Friday.