The US bid to extradite Megaupload founder Kim Dotcom has suffered a knock back.

A New Zealand judge has upheld a decision that the US Government must reveal the information it has gathered about Dotcom which forms the basis of its court case in the US against him.

The United States had sought to judicially review the decision saying it was unprecedented in New Zealand law. It said there was no requirement to reveal its case to Dotcom as it pursued an order to have him extradited back to the US to face copyright charges.

This afternoon Justice Helen Winkelmann dismissed the application for review saying without disclosure Dotcom and his co-accused would be considerably constrained in their ability to defend an extradition hearing.

Lawyer John Pike, acting for the US government, had earlier told Justice Winkelmann that it didn't have to disclose all this information as it needed only to prove its case was strong enough that a jury could reasonably convict Dotcom and his co-accused.

This comes after Dotcom's legal team, earlier today appeared in the High Court at Auckland seeking more access to his money so he could pay legal fees that could run to nearly $5 million.

The team asked to borrow against his frozen $10 million worth of New Zealand government bonds, saying he had already run up legal bills of around $2.7 million.

Dotcom has successfully applied for access to some of his funds, and was granted a monthly allowance of $20,000 in April.

Akel also argued that a number of Dotcom's cars, which he said had lost half their value, should be put on the market to raise costs.

These could include his pink 1959 Cadillac convertible and 1957 Cadillac El Dorado.

Dotcom, 38, is currently on bail awaiting an extradition hearing.

Authorities say he and his three co-accused - Mathias Ortmann, Fin Batato and Bram Van der Kolk- used Megaupload and its affiliated sites to knowingly make money from pirated movies and games.

Dotcom is charged with multiple copyright offences.