NSW Police Commissioner Mick Fuller has confirmed there has been a raid on the Ruby Princess under order by the state coroner.

Key points: More than 1,000 crew remain on board the stricken vessel, 200 of whom have flu-like symptoms

More than 1,000 crew remain on board the stricken vessel, 200 of whom have flu-like symptoms The Ruby Princess has been linked to more than 600 coronavirus cases and 15 deaths

The Ruby Princess has been linked to more than 600 coronavirus cases and 15 deaths The ship is docked at Port Kembla but will leave for Bermuda next week

He said investigators who boarded the ship on Wednesday evening had spoken to the ship's captain who was "extremely helpful".

"Ships have a black box very similar to that of international planes and that and other evidence has been seized for further investigation," he said.

Commissioner Fuller said there were still more than 1,000 crew on the ship, three-quarters of whom want to stay on the vessel.

"They feel safe on the ship, and I think that's a good outcome."

The ship is docked at Port Kembla, south of Sydney.

The vessel is at the centre of a COVID-19 criminal investigation into whether its operator downplayed the number of potential coronavirus cases on board, before it was allowed to dock in Sydney on March 19.

About 2,700 passengers disembarked from the ship and it has since become the largest source of coronavirus infections in Australia.

More than 600 cases of COVID-19 and 15 deaths are linked the to the ship.

The 1,000 crew remaining on the ship are from 50 different countries.

About 200 are displaying flu-like symptoms and 18 have been diagnosed with coronavirus.

Strike Force Bast investigators entered the Ruby Princess on Wednesday night. ( Supplied: NSW Police )

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Commissioner Fuller announced the criminal investigation would probe the communications, actions and other circumstances that led to it docking at Circular Quay.

A team of 30 investigators have been seconded to Strike Force Bast to conduct the inquiry.

The strike force includes intelligence analysts and other specialist officers.

The ship moved to the Illawarra region on Monday morning.

International Transport Workers Federation national coordinator Dean Summers said he was worried about the treatment of the workers on board.

"Get them off the ship and isolate them somewhere else," Mr Summers said.

"They just want to be treated like the passengers, like everybody else, with a bit of dignity."

Mr Summers said the ship should have remained docked in Sydney.

"Who would make a decision to send a ship with sick people on it away from three hospitals and towards a regional centre," he said.

"To try and hide it behind a coal stockpile and so the ship is going to be covered in coal dust and out of sight, out of mind, it is an unjustifiable position."

The vessel is due to leave Port Kembla and return to Bermuda in seven days.