WikiLeaks founder Julian Assange's extradition case has been delayed until September and will be moved to another court by a British judge.

The Australian's next hearing had been due on May 18, but District Judge Vanessa Baraitser last week agreed to delay it over concerns that Assange and lawyers would not be able to attend in person.

Judge Baraitser said as both legal parties were struggling to work out a new date in July, she would move the case to another Crown Court with better availability in September.

The new location and start date of the remaining three weeks will be confirmed on Friday by the court.

"It's going to take some negotiation to find a Crown Court that is open in September, in the current climate, and willing and available to take this hearing," Judge Baraitser said.

Assange did not attend as he was too unwell.

Judge Baraitser said there would be a callover hearing on June 1 if the Australian was well enough.

The 48-year-old faces 17 charges of violating the US Espionage Act and one of conspiring to commit computer intrusion.

He is accused of publishing thousands of secret US diplomatic and military files, some of which revealed alleged war crimes in Iraq and Afghanistan.

The charges carry a total of 175 years' imprisonment.

AAP

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