Footage from within one of Australia's offshore detention facilities for asylum seekers reached its first international audience this week in London, with one of the filmmakers highlighting the plight of his co-director who remains inside the camp.

"Chauka, Please Tell Us The Time" portrays life within Papua New Guinea's Manus Island camp, built as part of Australia's immigration crackdown which has seen asylum seekers who try to reach the country by boat taken to an offshore site.

The footage was shot on a smartphone by Behrouz Boochani, an Iranian who has spent four years in the camp since the boat he was trying to reach Australia on was intercepted by the authorities.

"We build the story with WhatsApp footage, really low-quality video, and it took a long time to transfer," said co-director Arash Kamali Sarvestani, who originally contacted Boochani through Facebook asking him to film inside the camp.

The outcome includes playful scenes of children on the other side of the fence and a scrawny cat, shot alongside those of men recounting their treatment and of ambulances arriving to treat detainees.

The film's title is a reference to the camp's solitary confinement cells, nicknamed "Chauka" after a type of bird native to Manus Island.

"We just talked about the ideas and then he found it in his own way because he's living there," Kamali Sarvestani told AFP during the London Film Festival.

Boochani is one of 1,000 people spread between the Manus facility and one on the island of Nauru, many of them from Iran, Afghanistan and Pakistan.

There has been a push to relocate the detainees to third countries after the country's Supreme Court ruled last year that holding people on the island was unconstitutional and illegal.

A first group of refugees from the Pacific camps was approved for resettlement in the United States in a deal struck with Washington under former president Barack Obama.

The pact has angered President Donald Trump, who has begrudgingly agreed to accept an unspecified number of people who can fulfil rigorously vetted requirements.

But it remains unclear what will happen to those not taken by the US.

- 'If he can get out...' -

Three men held at Manus have died, and the filmmakers hope that seeing the inside view of the camp's conditions -- widely criticised by refugee advocates and medical professionals -- will have an impact on audiences.

"This is the first place that the movie is screening outside Australia, so we can test it if it works or not; if people from other countries become angry or put pressure on Australia," Kamali Sarvestani said.

Boochani had been invited by the British Film Institute to attend the screening of his film, with the festival hosts praising the documentary as "brave, thoughtful and urgent filmmaking".

But despite writing to the British High Commissioner to Australia, Menna Rawlings, requesting help in coming to London, Boochani remains on Manus.

Kamali Sarvestani said his co-director is stuck in limbo, unable to go back to Iran but with no third country willing to accept him.

"If he can get out of that camp I think he will have a great life in the future, but I don't know. I really hope he can leave, but I think it would be difficult," he said. afp