Authorities in Nevada are treating the death of a man at the Burning Man festival as suspicious.

Shane Billingham, 33, was found unresponsive in his car at around 18:30 local time on August 29.

According to police, the New Zealand national had “poisonous” levels of carbon monoxide in his blood.

Bystanders reportedly attempted CPR on Shane Billingham before paramedics arrived.

The man was taken to a medical tent, where he was later pronounced dead.

Pershing County Sheriff’s Office said it was investigating the death as suspicious.

A post-mortem examination found Shane Billingham had “a concentration of carbon monoxide in his blood which would be considered poisonous to human life”.

The Washoe County medical examiner’s office said: “Preliminary toxicology showed the presence of controlled substances to be an exacerbating factor.”

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A makeshift memorial for Shane Billingham has been set up at Beats Boutique, the camp where he was staying at the festival.

One of his friends, Steve MacWithey, told the Reno Gazette Journal he had been “one of the best people” he had ever known.

Shane Billingham’s sister has launched an online fundraising page to help with the costs of bringing his body home.

Burning Man is a music and arts festival held annually in the Black Rock Desert of northwest Nevada, approximately 100 miles away from Reno.

Taking place between 25 August and September 2, the Burning Man festival – attended by tens of thousands of people – describes itself as “a temporary metropolis dedicated to community, art, self-expression, and self-reliance”.