Kim Dotcom, the founder of the Megaupload online file-sharing site.

Wellington - An extradition hearing for the founder of the file-sharing Megaupload website and accused internet pirate Kim Dotcom has been delayed until next year because of the complexity of the case.

US authorities want to extradite Dotcom and three co-defendants to face racketeering, copyright and money-laundering charges involving millions of dollars.

A three-week extradition hearing had been set for August in the High Court in Auckland, but it has been deferred until March 25 after a series of legal battles. They included one that ended with a judicial declaration that the warrants used to raid and seize Dotcom's property in January were unlawful.

New Zealand authorities are also challenging another ruling that they have to disclose evidence against Dotcom, a German-born New Zealand resident, and his three co-accused - Mathias Ortmann, Fin Batato and Bram van der Kolk.

They have denied the charges against them, which carry sentences of up to 20 years if they are convicted. - Sapa-dpa