New Zealand's Supreme Court on Thursday granted Kim Dotcom leave to appeal a ruling that US authorities do not have to disclose all of the evidence they have against the Megaupload founder.

The Court of Appeal in March had overturned a decision ordering US prosecutors to hand over the evidence to Dotcom's legal team as they seek to extradite him to face online piracy charges.

The appeal court ruled that a summary of the case would suffice.

Dotcom's lawyers have sought to reinstate the original decision, arguing they could not effectively fight the extradition battle without full disclosure of the evidence against their client.

The Supreme Court agreed to hear Dotcom's legal challenge at a date yet to be set. "Leave to appeal is granted," it said in a two-paragraph ruling.

Lawyers representing the United States had argued in the appeal court that the evidence could involve billions of emails and that full disclosure would likely delay Dotcom's extradition hearing, scheduled for August.

The US Justice Department and FBI want Dotcom to face charges of racketeering, fraud, money-laundering and copyright theft in a US court, which could see him jailed for up to 20 years if convicted.

Dotcom is free on bail. He denies US allegations the Megaupload sites netted more than US$175 million in criminal proceeds and cost copyright owners more than US$500 million by offering pirated copies of movies, TV shows and other content.

The German national, who was arrested in an armed police raid on his Auckland mansion in January last year, launched a successor to Megaupload called Mega in January this year.