WikiLeaks founder Julian Assange's US extradition case will be delayed over concerns about his ability to attend hearings in person amid the UK's coronavirus lockdown.

District Judge Vanessa Baraister has adjourned the case until May 4 so lawyers can work out a new date for the next hearing, which could be as late as November 2.

Assange is battling to avoid extradition to the US to face charges of violating spy laws and computer intrusion.

The Australian's lawyers argued there were a raft of reasons to delay the case in the Westminster Magistrates Court on Monday.

But Judge Baraister was only convinced by one: the potential inability for Assange and lawyers to attend the planned May 18 hearing in person.

"Remote attendance by the parties in this case will not be appropriate," she ruled.

"It is now appropriate to vacate that hearing and fix it to a later date."

Barrister Edward Fitzgerald had argued that, apart from brief phone calls, defence lawyers hadn't spoken with Assange for over a month.

He said they were due to meet him in the holding cells of Woolwich Crown Court last week but prison authorities wouldn't allow it.

"With the coronavirus outbreak the preparation for this case goes from difficult to impossible," Mr Fitzgerald told the court.

"There are no person-to-person meetings. The alternative of video conferences is medically dangerous.

"Mr Assange will be facing a David and Goliath battle with his hands tied behind his back."

The barrister argued that the lockdown prevented witnesses from attending in person and the press from monitoring proceedings.

Mr Fitzgerald also raised the advice of Chief Magistrate Emma Arbuthnot on extradition hearings earlier this month.

He said the senior judge had recommended extradition hearings only occur by videolinks if both parties agree to it.

"In this case both the prosecution and defence agree that it would not be fair to proceed with this hearing by videolink," he said.

Judge Baraister couldn't see how the lockdown would affect case preparation, witness attendance or press reporting.

However, she granted the delay because the physical attendance of Assange and both legal teams on May 18 was in doubt.

Assange's father John Shipton hopes he will apply for bail soon to protect his health.

"So Julian can come home to his family and children rather than being in constant danger of having a lung infection in a COVID prison where two people have died of the disease," he told AAP outside court.

"It's just wrong, it's just wrong, he's an innocent man on remand."

Shipton added that Assange should be with his fiancee and two young sons.

"They do need their father, they do need him very soon," he said.

Judge Baraister denied a bail application two weeks ago, when his lawyers argued Assange was in danger of contracting the coronavirus in prison.

Assange faces 17 charges of violating the US Espionage Act and one of conspiring to commit computer intrusion.

He's 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.