A 29-year-old Canadian allegedly stabbed to death a British tourist after the two drank a hallucinogenic brew at an Amazon spiritual retreat in Peru.

Authorities said the incident happened on Wednesday night at the Phoenix Ayahuasca retreat near the town of Iquitos.

It is not clear what led to the death of Unais Gomes, 25, but police chief Normando Marquez said witnesses described a fight breaking out between Mr Gomes and fellow tourist Andrew Freeman during which a knife was pulled against the Canadian. The same knife was then used by Mr Freeman to kill Gomes, the chief said.

In a video, Mr Freeman can be seen being taken away in custody by a police truck. He was later released but must remain in Peru while he is being investigated for murder.

The hallucinogenic cocktail ayahuasca, also known as yage, has been venerated for centuries by indigenous tribes in Brazil, Peru, Ecuador and Colombia as a cure for all sorts of ailments.

But it is also increasingly consumed by Western tourists looking for mind-altering experiences, sometimes with deadly consequences.

The two men were guests at Phoenix Ayahuasca, a self-described "shamanic healing retreat" owned by a sister and brother team from Australia.

It describes itself on its website as "a safe and supportive place to experience plant medicines and explore the true nature of the self".

Phoenix did not return requests for comment.