A woman has spoken of her horror at seeing a man fall to his death and his partner writhe in agony when a zip-line snapped in Far North Queensland on Tuesday.

Key points: A 50yo man died after falling more than 10 metres at the Jungle Surfing Canopy Tours

A 50yo man died after falling more than 10 metres at the Jungle Surfing Canopy Tours Mardi Liebelt was standing behind the couple when the accident happened

Mardi Liebelt was standing behind the couple when the accident happened She says she had no safety concerns about the equipment on the day

Dean Sanderson, a 50-year-old man from Adelaide, died after falling more than 10 metres at the Jungle Surfing Canopy Tours in the Daintree Rainforest, north of Cairns.

His 48-year-old wife Shannon — who was in a separate harness but launched at the same time — also fell and is in a serious condition at the Cairns Hospital.

Dean and Shannon Sanderson have been identified as the victims of the accident. ( Facebook: Shannon Sanderson )

Witness Mardi Liebelt, from Hervey Bay, was behind the couple and about to take her turn when she said the line snapped.

"The twang when the zip-line came back up made an awful noise, then there was just silence for what seemed like forever," she said.

"And then the lady was just screaming for help, a terrible blood-curdling scream that I never wish to hear again.

"There was a gentleman who had just gone across the zip-line, as a customer, he was a paramedic and so he got down and went to help.

"He managed to revive him for a while [the victim] but he died because of massive head trauma."

Jungle Surfing director Phoebe Kitto said the company was offering counselling to staff and patrons. ( ABC News: Marian Faa )

Ms Liebelt said she and her husband spent the next hour stranded on the sky-high platform until they were helped down with ropes.

She said staff and everyone else who witnessed the accident were in a state of shock.

"I broke down into tears, I was sweating," she said.

"They were a very friendly couple, enjoying themselves.

"Ironically they were telling us how they had zip-lined in Bali and how there's not much in the way of safety there and how they felt much safer being back in Australia and zip-lining."

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Ms Liebelt said she had no safety concerns about the state of the equipment on the day.

"Our harnesses were very secure, the staff seemed to know their job," she said.

"They were counting and re-counting the clips that they put on you to go to the next zip-line, we had helmets, the actual equipment was very safe."

Ms Liebelt said it could have been her that was killed.

The attraction is run by Jungle Surfing Canopy Tours. ( Facebook: Jungle Surfing Canopy Tours )

"We feel guilty, we feel lucky, we have felt every emotion in between and still do.

"We don't know why it was them and not us.

"We obviously had guardian angels.

"We haven't slept, every time you shut your eyes you relive it because you see it again.

"Why wasn't it us, why was it them?"

Ms Liebelt said the company took nearly 20 hours to phone them to offer their condolences and support.

A man rides the zip-line upside down in Daintree rainforest on February 10. ( Facebook: Jungle Surfing Canopy Tours )

Phoebe Kitto, a Director of Jungle Surfing, offered her deepest sympathy to the families and friends of those affected.

"It will be thoroughly investigated by Workplace Health and Safety, which will receive our full cooperation," she said.

"We are offering counselling to staff and to our patrons."

Tourism Minister Kate Jones also passed on her condolences, adding Government tourism bodies would provide support to the operators and its staff.

"I can assure all members that the tourism operators will comply fully with the police and also with Workplace Health and Safety in their investigations," she said.

Two people on the zip-line earlier this year. ( Facebook: Jungle Surfing Canopy Tours )

Douglas Shire Mayor Julia Leu said an incident like this impacts the whole community, which is reliant on tourism.

"It is a beautiful township and I know that this will affect many people in Cape Tribulation," she said.

"We're extremely sad about what has happened. It is a real tragedy and our hearts go out to family and friends."