Megaupload boss Kim Dotcom will appeal Friday against a ruling that kept him behind bars in New Zealand while US officials seek his extradition for alleged copyright piracy, his lawyers said.

The German millionaire was refused bail last week when a judge ruled that he posed a serious flight risk because he had the money and shady connections to slip out of the country.

Dotcom was remanded in custody until February 22 but a spokeswoman for his lawyer Paul Davison told AFP on Thursday that an appeal would be heard in Auckland High Court on Friday.

She declined to give further details, although a High Court official confirmed the hearing was scheduled for Friday.

The founder of the file-sharing website Megaupload.com has been in detention since New Zealand police, cooperating with a major US probe, raided his sprawling "Dotcom Mansion" in Auckland on January 20.

Davison argued at his client's original bail hearing that Dotcom, who spent his 38th birthday behind bars, should be released to prepare his defence.

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.

Davison also said Dotcom was on medication for diabetes and hypertension, adding that there was no danger he would flee because his assets had been frozen and his family remained in Auckland.

Refusing bail, Judge David McNaughton raised concerns that Dotcom had bank accounts and passports in different names and may try to escape to Germany, which does not extradite its citizens to the United States.

He also said an unlicensed, sawn-off shotgun found in a "panic room" to which Dotcom retreated when police swooped on his home raised the possibility that the Internet tycoon had criminal connections who could help him flee.

The raid on Dotcom's home netted a 1959 pink Cadillac, numerous other luxury cars and valuable artworks -- all of which the US Justice Department and FBI allege was obtained through "massive worldwide online piracy".

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