Novak Djokovic's family and fans have railed against the superstar's shock detention in Australia, which left the world tennis number one spending Orthodox Christmas Day on Friday in a Melbourne immigration detention facility.

In a series of fiery remarks, his father Srdjan Djokovic told a crowd in Belgrade that his son was the victim of a "political witch hunt" and "corona fascism" and should be freed.

Fans chanted "free Novak" outside Melbourne's Park Hotel which now serves as a detention centre. Draped in flags and defying the rain, protesters played nationalistic Serbian songs. Some held anti-vaccine placards, while others rallied in support of refugees.

The vaccine-sceptic tennis ace was detained on arrival in Australia earlier this week -- his visa was revoked for failing to meet Australia's tough pandemic entry restrictions.

Foreigners are still mostly banned from travelling to Australia and those granted permission to enter must prove they are fully vaccinated or have a doctor's medical exemption.

Australian authorities said the controversial Serbian star -- who has declared himself against vaccines and claimed to have an exemption -- provided evidence of neither and was detained, pending deportation.

Djokovic "met all the required conditions for the entry and participation at the tournament that he would have certainly won," his father insisted.

"Jesus was crucified and endured many things but is still alive among us," he said on Orthodox Christmas Eve. "Novak is also crucified... the best sportsman and man in the world. He will endure."

His mother Djina Djokovic told television reporters at the rally: "They are keeping him as a prisoner. It is just not fair. It is not human. So I just hope that he will be strong as we are trying also to be very strong."

Wrong court

Djokovic landed at Melbourne's Tullamarine Airport on Wednesday hoping to defend his Australian Open crown and seal an unprecedented 21st Grand Slam title.

Although Djokovic won a legal reprieve from deportation until at least Monday, when his case will be heard in court, it is far from clear that he will play in the January 17-30 tournament.

Judge Anthony Kelly warned the star's lawyers in a hearing Thursday that justice would move at its own pace through all necessary appeals. "The tail won't be wagging the dog here," he said.

Two other players or staff attending the Australian Open are also now being investigated, Home Affairs Minister Karen Andrews confirmed Friday.

She also denied allegations that Djokovic was being held against his will.

"Mr Djokovic is not being held captive in Australia. He is free to leave at any time that he chooses to do so and Border Force will actually facilitate that," she said.

Australian authorities have repeatedly refused to confirm where they are holding the Serbian star, but he is believed to have spent the night at what is officially known as the Melbourne "Alternative Place of Detention".

The facility, once a hotel, is home to around 32 refugees and asylum seekers who have been trapped for years in Australia's hardline immigration system.

Detainees cannot leave the hotel and nobody is allowed in or out except staff.

‘Maggot hotel’

The facility gained notoriety last year when a fire in the building forced refugees and asylum seekers to be evacuated, and maggots were allegedly found in the food.

As word of Djokovic's arrival spread, Serbian flag-festooned supporters, anti-vaccine campaigners, refugee advocates and police descended on the already controversial facility.

Detainee Mehdi Ali told AFP that Djokovic is his favourite tennis player, and that he was saddened by the prospect of the star being held there.

"The media will talk about us more, the whole world probably, which is so sad, just because Djokovic would be here for a few days," he said.

Djokovic's detention has sparked international scrutiny and a serious diplomatic incident, with the Serbian government demanding explanations.

"Djokovic is not a criminal, terrorist or illegal migrant, but was treated that way by the Australian authorities which causes an understandable indignation of his fans and citizens of Serbia," a foreign ministry statement said.

The country's president, prime minister and foreign minister have all issued a series of nationalist-tinged remarks brimming with anger at the treatment of a national hero.

‘Rules are rules’

In Australia, the country's conservative prime minister is facing questions about how the incident was handled ahead of a looming election.

Scott Morrison -- under pressure from soaring Covid case numbers and the collapse of the once-excellent testing system -- has defended revoking Djokovic's visa at the last minute.

"Rules are rules and there are no special cases," he said.

But many Australians, angry at seeing 70,000-plus new Covid cases a day after two mostly Covid-free years, see the Djokovic case as a diversion.

"This is happening while we've got a major crisis going on in terms of Omicron, and it's been convenient from the government's point of view" Australian Medical Association vice president Chris Moy told AFP Friday.

John Findley, an Australian immigration lawyer, said both the state and Djokovic would have to answer some tough questions in court.

"If they see (Djokovic) has provided false information, he must have a chance to answer that," Findley said.

That charge, if proven, could bring a three-year ban from applying for another Australian visa.

But Findley also said the visa revocation seemed to have come from "a pile-on from social media" and the government would need to explain the legal bar that Djokovic failed to meet.