Emergency crews were called to Heron Road at Kooragang - Newcastle harbour - about 9.30am on Monday, where they found a man with more than 50kg of the illicit drug in the immediate vicinity.

Police said on Tuesday morning the diver had been found unconscious in the water at Berth Two of the Port of Newcastle, and members of the public performed CPR on him - but he died at the scene.

The cocaine is believed to have a street value of $20 million.

It is not yet clear how exactly the diver got into trouble before his death.

NSW Police Organised Crime Squad commander Detective Superintendent Robert Critchlow said the man remained unidentified after checks through all available Australian databases.

Detective Superintendent Critchlow said investigators were also searching for information about an inflatable rubber duck-style vessel and a five metre aluminium Quintrex runabout with a green stripe seen in the area about midnight on Sunday.

He said the cause of the diver's death was not clear but he was wearing a rebreather, described as "a specialised piece of diving equipment used by people with high levels of training".

Police are investigating the possibility that the drugs were brought into Australia strapped to a ship from the Marshall Islands Port of Maduro - Aret. G Majuro - which appears to have left Argentina about a month ago.

The ship remained in the port on Tuesday morning but was expected to be able to continue its journey on Tuesday night - all crew have been interviewed by police.

Australian Border Force Acting Superintendent Anthony Wheatley said 50kg of cocaine was "a significant amount".

Superintendent Wheatley said underwater drug concealment was seen worldwide and, in most cases, the crew of the vessel transporting the drugs were doing so unwittingly.

Detective Superintendent Critchlow said the high street value of cocaine in Australia made it an attractive target for international traffickers.

"We have detected this methodology on and off over the years," he said.

"Often the ships are innocent agents - they're utilised by crime groups to bring in the drugs unawares.

"It's a high-end sophisticated operation, they're looking at moving commodities and people across the world.

"The high retail price in Australia is a huge draw for international traffickers and they're targeting our community with this poison to sell for a profit.

"To put on a shipment of this scale is quite a complicated arrangement and done very very professionally."

Detective Superintendent Critchlow said police had been "aware of Newcastle port being a drug shipping port for some time".

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"There have been some indications in the past of OMCG [outlaw motorcycle gang] involvement around the docks, and again we've worked very closely with our partners to remove them from the system," he said.

"It remains a point of risk because any port has a lot of movements - so a lot of ships, a lot of trucks, a lot of people, so it is easier to hide drugs amongst that.

"We are certainly concerned about the ports of Newcastle and Wollongong and organised crime definitely looks for weaknesses to target those points."

Marine Area Command investigators and police divers were continuing their search for more clues on Tuesday.

The Organised Crime Squad and Australian Federal Police are also investigating the matter.

The diver is expected to be examined by the Coroner on Tuesday.

Detective Superintendent Critchlow said it was a concern that there appeared to be more people than the dead man involved in the operation at Berth Two, but that he appeared to have been "left for dead".

"The presence of two boats indicate at least two other people," he said.

"It's quite disgusting this man has been left to die, regardless what he was involved with."