Additionally, the ship may not leave Port Kembla this Thursday as planned.

Last Thursday , 97 crew showing symptoms of possible infection were tested.

Of those 46 tests - 49 per cent - came back positive and 50 were negative; one test was yet to be returned as of Friday night.

Overall 52 people still onboard have COVID-19, while 11 people have been taken off the Ruby Princess and entered NSW hospitals.

"These results are not unexpected," said a statement from NSW Health, "and in many cases represent resolving illness and part of the attempt to allow critical staff onboard to return to work and prepare the vessel for departure as well as support their colleagues still in isolation onboard the vessel."

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In the wake of these results, NSW Health said further testing of crew will take place.

"Further and increased testing will occur over the next few days as NSW Health, Aspen Medical and Australian Border Force work to improve infection prevention and control and fully investigate all those with symptoms," the statement read.

"While more positive cases may be found, the measures now put in place will ensure that new infections are halted and those with the illness continue to be supported to recover onboard the vessel, accessing emergency medical treatment onshore when required."

The ship was quarantined in Port Kembla for 10 days - it is scheduled in the port's shipping movements to leave on Thursday.

While that was still the plan, NSW Health Minister Brad Hazzard said on Sunday that the ship may be in port for longer.

"These things are fluid," Mr Hazzard said.

"If there are issues upon that ship that need to be looked at, obviously we're not going to send that ship out to sea.

"The intention is certainly to get them on their way, when it is humanitarianly acceptable and we can be sure that all those people are being well looked-after."

The decision to increase testing will be welcome news to both unions representing the crew and Labor's Health spokesman Ryan Park, who have been calling for a heightened testing regime.

"This is a tragedy - 15 people from this ship have died," Mr Park said.

"That's more than the Waterfall and Glenbrook train accidents combined. Those disasters resulted in a Special Commission of Inquiry

"There are 408 infections linked to the Ruby Princess in NSW alone. We have been consistently asking for everyone on board to be tested. We cannot afford to be complacent."

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