Mystery surrounds the identity of a dead diver and 50 kilograms of cocaine found floating in the water near the NSW Port of Newcastle.

Police have not yet identified the man, despite running him through various databases after he was found unconscious and later died.

They are investigating whether he was a drug mule linked to an international drug syndicate whose job was to retrieve the bricks of cocaine from a ship or the ocean floor.

He was found unconscious about 9.30am on Monday by port officials, before police later spotted packages containing the white powder with an estimated street value of $20 million.

Police are investigating whether the drugs came from the nearby cargo ship Areti, a Marshall Islands vessel that arrived in Newcastle from Argentina on Sunday.

Two boats – a rubber dinghy and an aluminium runabout – were also seen near that ship on Sunday night.

The dead diver had sophisticated equipment, NSW Police Detective Superintendent Rob Critchlow said on Tuesday.

That included a “rebreather” apparatus that lets divers breathe underwater without the telltale bubbles of less sophisticated scuba equipment. The specialised gear has a price tag that runs into five figures.

Detective Superintendent Critchlow has appealed for any dive shops that may have sold the equipment, or a Sharkskin brand wetsuit, to contact police.

Australian Border Force officers had been searching the Areti for the past 24 hours, ABF Acting Superintendent Tony Wheatley said.

The ABF screened all ships and their crew when they arrived in Newcastle, he said.

The crew has also been interviewed and the vessel likely will be allowed to leave the port in the next 24 hours.

The port had been under police scrutiny for some time, Detective Superintendent Critchlow said.

“There have been some indications in the past of [outlaw criminal motorcycle gang] involvement around the docks,” he said.

“It remains a point of risk … and organised crime definitely look for weaknesses to target those ports.”

Using divers to retrieve shipments from the hulls of ships has been used on and off by drug traffickers for years.

If the dead diver is linked to the drug shipment, it’s assumed he wasn’t acting alone.

“These people have fled so it’s quite disgusting that this man’s been left to die regardless of what he was involved with,” Detective Superintendent Critchlow said.

Police divers continued to search surrounding waters on Tuesday, with help from Australian Border Force officers.

Queensland University of Technology associate professor of justice Mark Lauchs said drug gangs would use any technique they thought would work.

Drug traffickers might have a different idea about whether the risk was too high, Mr Lauchs said, because enforcement only looked at supply of drugs, not demand.

“If people have the money, they will just pay more money, attracting more sellers,” he said.

Legalisation was not necessarily a solution either.

The high taxes a regulated drug market would inevitably attract would open new avenues for criminals to continue importing illegally, similar to what had happened as taxes on tobacco increased.

“They will move in to a different way of making money off the same product,” Mr Lauchs said.

-AAP