Megaupload founder Kim Dotcom must be given access to materials that U.S. authorities plan to employ in pursuing his extradition from New Zealand, a trial court said on Thursday.

NZ Justice Helen Winkelmann cited the country's Bill of Rights in handing down a ruling that again provided traction to Mr Dotcom's quest of clearing his name following the raid of his swanky mansion near Auckland January this year.

That operation and the former hacker's subsequent arrest were earlier declared illegal by the same NZ court, which reprimanded authorities involved for using what were later concluded as defective warrants.

And yesterday's decision by Justice Winkelmann also upheld the basic functions of legal proceedings that she noted must be extended to Mr Dotcom if only to ensure that he gets a fair trial once the extradition case filed against him by U.S. authorities begins playing out on March 2013.

In her ruling, the NZ judge stressed an earlier decision by the first justice who handled the high-profile case: "There must be fairness and the hearing and balance must be struck."

"Otherwise the record of case becomes dominant virtually to the exclusion of everything else and places the extradition process in danger of becoming an administrative one rather than judicial," tech blog site TorrentFreak quoted the same ruling as saying.

Prosecutors immediately sued for a review but Justice Winkelmann turned down the plea, saying that denying the Megaupload defendants access to evidences that will be arrayed against them was tantamount to convicting them minus the application of due process.

"Without access to materials relevant to the extradition hearing phase, the person sought will be significantly constrained in his or her ability to participate in the hearing," Reuters reported the ruling as saying.

"To attempt to control (evidence disclosure) by severely constraining the information available to the person sought (in this case Mr Dotcom and his co-accused) is to use a very blunt instrument and risks an unfair hearing," the court ruling further explained.

The court also argued that disclosures would only amount to what are relevant to the extradition case that Mr Dotcom and his Megaupload colleagues need to face next year, which downplayed U.S. fears that such access could lead "to an unprecedented general disclosure of information."

Justice Winkelmann noted at the same time that present form of documents pertaining to the extradition case still fall short of standards set by New Zealand laws.

Shortly after the ruling was made public, Mr Dotcom petitioned a separate court to give him access to his assets, which were under hold since his arrest in January on accusations by the U.S. Justice Department that Megaupload had facilitated the illegal exchanges of online contents that led to copyright infringements, costing American producers some $US500 million in losses.

U.S. authorities also alleged that Mr Dotcom's criminal activities had amassed for him some $US175 million.

The Megaupload owner has consistently denied the charges, insisting that his online business, shuttered down since the raid, was merely to provide online storage to millions of users.

Lawyers for Mr Dotcom have asked NZ authorities to unfreeze at least $NZ10 million, the Australian Associated Press (AAP) reported on Friday, which will be used to pay for his legal expenses, now running at around $3 million, and other necessities.