Dr Michael Guillen was one of the first journalists to be taken to the wreck, two-and-a-half miles below the Atlantic's surface.

On board a Russian vessel, he toured the Titanic's divided remains.

The bow posed no problems for the crew, but towards the stern the submersible encountered a high-speed underwater current which slammed them into the giant propellers, where they became trapped.

Speaking to Sky News, Dr Guillen said: "Our sub was like a giant mosquito compared to the propeller. Huge pieces of the Titanic started falling down on us and I knew we were in trouble."

'The end'

Dr Guillen said he could feel the fear rising in him and recalled a story of a man who was caught in a similar situation, panicked and opened the escape hatch, only to be "expedited to his doom".

He said: "The pressure down there of the water even if through a little crack - it will cut you like a razor blade."

After the best part of half an hour, Dr Guillen hit a brick wall and thought it was "the end" for him.

"There was a voice in my head. I'll never forget the words - 'this is how it is going to end for you'. I thought of my wife who I'd never see again. I don't like recalling that experience."

The scientist survived the ordeal thanks to the pilot being able to manoeuvre free.

'My heart goes out to the people who are lost'

Dr Guillen fought back tears as he thought of the five men trapped in the missing Titan.

He said: "My heart goes out to the people who are lost. I'm sick to my stomach to think [of them] down there."

Certain aspects of the incident struck Dr Guillen as concerning - one being the dropout in communications in under two hours suggesting they didn't reach the sea bed before the failure.

"If it was a communications failure then you would know for sure that the pilot of that sub would have headed straight up to the surface. The fact he hasn't really concerns me."

Read more:
Titanic submersible: Missing craft may have imploded

'This is not a Disneyland ride'

The scientist condemned the mission taking place in what he described as an "experimental craft".

He said: "This is not a Disneyland ride. This is Mother Nature. The ocean is unforgiving.

"Everything is opening up to tourists and I fear when there is money involved and profit to be had with thrill seekers out there willing to ante up the money, that is a recipe for disaster.

"I am hoping this is not how this story is going to end."

The five on board the missing submersible had "about 40 hours of breathable air" left, the US Coast Guard said on Tuesday night.

They are British billionaire Hamish Harding, Pakistani businessman Shahzada Dawood and his son Suleman, chief executive and founder of OceanGate Expeditions, Stockton Rush, and French submersible pilot Paul-Henri Nargeolet.

A major search and rescue operation is taking place some 435 miles south of Newfoundland, Canada.

The wreckage of the Titanic, which sank in 1912 after hitting an iceberg, lies at a depth of about 12,500 feet (3,810 metres).