Assange has spent more than eight years either holed up in London's Ecuadorean embassy or in jail.

But on Monday he won an attempt to stop his extradition to the United States to face 18 criminal charges of breaking an espionage law and conspiring to hack government computers.

He had then asked to be bailed.

"I am satisfied that there are substantial grounds for believing that if Mr Assange is released today he would fail to surrender to court to face the appeal proceedings," Judge Vanessa Baraitser said.

The US Department of Justice says it will continue to seek Assange's extradition.

"As far as Mr Assange is concerned this case has not yet been won ... the outcome of this appeal is not yet known," the judge said.

Admirers hail Australian-born Assange as a hero for exposing what they describe as abuses of power by the United States.

But detractors cast him as a dangerous figure who has undermined the security of the West, and dispute that he is a journalist.

WikiLeaks published hundreds of thousands of secret diplomatic cables that laid bare often critical US appraisals of world leaders, from Russian President Vladimir Putin to members of the Saudi royal family.

Assange made international headlines in early 2010 when WikiLeaks published a classified US military video showing a 2007 attack by Apache helicopters that killed a dozen people in Baghdad.

In June 2012, Assange fled to London's Ecuadorean embassy after losing his bid to prevent extradition to Sweden, where he was wanted for questioning over alleged sex crimes.

He remained in the embassy, in confined conditions, until dragged out in April 2019.

Although the Swedish case against him had been dropped by then, he was jailed for breaching British bail conditions and his supporters forfeited sureties of Stg 93,500 ($A163,700).

Australian Associated Press