Megaupload boss Kim Dotcom is set to learn Wednesday if he will remain free on bail in New Zealand while US authorities seek his extradition on online piracy charges, reports said Tuesday.

The German national was released last week after a judge dismissed fears he would flee the country to escape US allegations he masterminded a "mega-conspiracy" involving massive online copyright theft.

Dotcom returned to court Tuesday as prosecutors appealed the ruling and sought to put him back behind bars, with television footage showing him wearing his customary black outfit and accompanied by his heavily pregnant wife.

After a day of legal argument, judge Timothy Brewer reserved a decision on whether to revoke the 38-year-old's bail and will announce his ruling on Wednesday afternoon, local media reported.

It was the portly millionaire's fourth bail hearing since New Zealand police, cooperating with the US investigation, raided his sprawling Auckland mansion on January 20.

At the first two, prosecutors successfully argued he was a serious flight risk, with the wealth and connections to slip out of the country if he wished.

But he was given bail in a surprise move last Wednesday, when a court accepted that it was in his interests to fight the case and seek to retain his assets, rather than abandon his family for a life on the run.

The US Justice Department and FBI allege Megaupload and related sites netted more than $175 million in criminal proceeds and cost copyright owners over $500 million by offering pirated copies of movies, TV shows and other content.

Megaupload was founded in 2005 but shut down last month when its assets were frozen as part of the US probe.

A US application for Dotcom's extradition is expected to be heard on August 20. US authorities have said they will seek the maximum penalty of 20 years in jail if he is brought before a US court.

Dotcom, who legally changed his name from Kim Schmitz, has denied any wrongdoing.