Megaupload boss Kim Dotcom's extradition case against US authorities has been delayed until next year amid legal wrangling in New Zealand over evidence disclosure, his lawyers said Tuesday.

A hearing to decide if the United States can extradite Dotcom from New Zealand to face online piracy charges was scheduled for August 6 but would now take place on March 25, a spokeswoman for his Auckland-based barrister said.

She said more time was needed to settle legal arguments relating to the extradition of the 38-year-old German national and three co-accused, part of a case US prosecutors have described as the world's largest copyright action.

Dotcom, who denies any wrongdoing, took to Twitter to complain about the hold-up, accusing US authorities of deliberately stalling the case.

"Dirty delay tactics by the US," he tweeted. "They destroyed my business. Took all my assets. Time does the rest."

Dotcom is free on bail after armed New Zealand police, cooperating with the US investigation, arrested him at his sprawling Auckland mansion in January.

At the same time, the FBI and US Justice department also shut down Megaupload and related file-sharing sites, which at their peak had 50 million daily visitors and accounted for four percent of all Internet traffic.

US authorities allege the Megaupload sites netted more than $175 million in criminal proceeds and cost copyright owners more than $500 million by offering pirated copies of movies, TV shows and other content.

Dotcom faces charges of racketeering fraud, money laundering and copyright theft, which could see him jailed for up to 20 years if convicted in the United States.

But the case against the Internet tycoon has suffered a number of setbacks in the New Zealand courts, leading to the delay announced Tuesday.

In May, the District Court said Dotcom had the right to see the evidence that would be used against him in a US court before the extradition hearing could proceed.

Then the High Court last month ruled the raid on Dotcom's mansion was illegal as the search warrants that police used were too broad.

New Zealand government lawyers acting on behalf of US authorities are expected to appeal both decisions ahead of the extradition hearing in March next year, which is expected to last for three weeks.

In the meantime, a US court is scheduled to hear a motion from Megaupload's lawyers on July 27 to dismiss all charges.