Taking the psychedelic drug ayahuasca and a frog toxin called kambo, a man suffering pain and facial swelling rejected calls for an ambulance before dying at an alternative spiritual retreat.

James Mackney attended the Dreaming Arts festival in Kyogle, northern NSW, along with Jarrad Antonovich who he said struggled to breathe after taking kambo and then swelled up so he "looked like a frog".

"To me, I was like far out this guy isn't looking good," he told an inquest on Thursday.

The 46-year-old died later the same day in the evening of October 16, 2021 after being ushered to a smoking ceremony where ayahuasca was taken.

Mr Mackney suggested calling an ambulance before the ceremony but said Mr Antonovich did not want one, instead believing his symptoms were part of a "purge" and that he had enough assistance from others attending.

Inside a temple as the ceremony started, Mr Antonovich could still be heard coughing and spitting up saliva outside, the inquest was told.

He was later brought inside and seated down surrounded by others wearing white. After he collapsed, CPR was performed while an ambulance raced to attend. Paramedics pronounced him dead at the scene.

An autopsy found he died of a perforated oesophagus.

Dentist Dr Marcus O'Meara participated in the ceremony and said he could hear Mr Antonovich struggling to breathe inside the temple as well.

When he turned towards the suffering man, a festival "guardian" blocked his view, ordering him to face the front and focus on the music playing.

Another attendee Robert Slabihoudek said he was concerned about the remoteness of the event if an emergency occurred.

"It was obvious that if some help is coming, it was going to be a while," he said.

Indigenous elder Uncle Andrew Johnston was invited to perform a smoking ceremony at the festival.

He saw Mr Antonovic lying down by a tree, complaining of back pain with a swollen neck.

Facing questions from the deceased man's family, Mr Johnston said he still personally supported the use of ayahuasca and kambo at these ceremonies as they were based on the traditional knowledge of the South American people spanning back thousands of years.

The elder said that while he was "upset" at what had happened, the circumstances surrounding Mr Antonovich's death were extremely unlikely and had "nothing at all do to" with the substances he took.

At the festival, which was held at Arcoora health retreat, attendees ingested a brew made with ayahuasca. They also had their skin burnt with kambo being rubbed into the wounds.

Typically, the chemical substance is scraped off the back of a live frog with a stick.

Professor Arthur Richardson, a medical specialist working at Westmead Hospital, said "repeated and severe vomiting" could cause an oesophagus to tear.

Ayahuasca and kambo, which are illegal in Australia, have been known to cause vomiting, with attendees at the retreat given buckets to throw up in.

Prof Richardson said a swollen neck could have been caused by gases escaping through Mr Antonovich's perforated oesophagus, and that 1.5 litres of water consumed during the kambo ceremony may have leaked out through the hole into his insides as well.

For someone attending hospital with a torn oesophagus, there was an 80 per cent chance of survival, the professor said.

The inquest, which continues on Friday, will examine how Mr Antonovich suffered the injury, whether this was caused by the drugs or something else, and what happened to him in the hours before he died.