Kim Dotcom's lawyer has lashed out during the internet mogul's extradition hearing, accusing the United States of "secrecy bordering on deceit".

Photo: RNZ / Kim Baker Wilson

Mr Dotcom and three other men face extradition to the US on copyright violation, money-laundering and racketeering charges related to their file-sharing website Megaupload.

The court is currently hearing stay applications from the men, to pause or even halt the extradition attempt altogether.

Mr Dotcom's lawyer, Ron Mansfield, told the court the summary of evidence presented by US authorities was one-sided and cherry-picked.

"In each case, the US seeks to draw the most sinister [conclusions]," he said.

The US had also refused to name many of the FBI witnesses it intended to call if the men faced trial and how they had obtained their evidence, Mr Mansfield said.

"Why, in this case, is there so much secrecy about who the evidence has come from and how it has been obtained?

"That's secrecy bordering on deceit," he said.

Photo: RNZ / Kim Baker WIlson

New Zealand's courts had found the US had a duty to be candid in its evidence, and the US was breaching natural justice by ignoring that, Mr Mansfield said.

At the same time, he said, the US had denied the defendants the ability to prove how selective its evidence was.

New Zealand and Hong Kong courts have ruled that Mr Dotcom can use his restrained assets to fund his legal case.

However, the US has threatened to seize any of those funds that are spent outside New Zealand - preventing the men from paying for any international expert witnesses.

The hearing is continuing.