Image copyright Getty Images Image caption Tens of thousand of revellers gather in the desert for Burning Man every year

The death of a man at the Burning Man festival in the US state of Nevada is being treated as suspicious, authorities say.

Shane Billingham, 33, was found unresponsive in his car at around 18:30 local time (00:30 GMT) on Thursday.

Mr Billingham, a New Zealand national, had "poisonous" levels of carbon monoxide in his blood, police said.

Bystanders reportedly attempted CPR on Mr Billingham before paramedics arrived.

He 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 Mr Billingham had "a concentration of carbon monoxide in his blood which would be considered poisonous to human life".

"Preliminary toxicology showed the presence of controlled substances to be an exacerbating factor," the Washoe County medical examiner's office said.

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

Image copyright Getty Images Image caption An aerial view of Burning Man festival in 2017

One of Mr Billingham's friends, Steve MacWithey, told the Reno Gazette Journal he had been "one of the best people" he had ever known.

Mr 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 (160km) away from Reno.

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

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