The Crown has confirmed it will appeal against the High Court ruling that search warrants used in a police raid on Megaupload founder Kim Dotcom's mansion were unlawful, a media report says.

The German national was arrested after police swooped on his Auckland home in January and stands accused of breaching copyright laws costing owners more than US$500 million. US authorities are attempting to extradite him to face the charges.

Justice Helen Winkelmann found in June that the warrants did not adequately describe the offences to which they related.