A woman, 79, has died on a cruise ship sparking concerns from her family she was a victim of a possible gastro outbreak.

Vanessa D'Souza claims her mother, Margaret Carlson, began showing signs of gastroenteritis after boarding the P&O Pacific Jewel Cruise ship in Sydney last Tuesday, the daughter told Sydney Morning Herald.

The 79-year-old from Terrigal on the NSW Central Coast was found dead in her room when the cruise ship docked at Yorkeys Knob in Cairns on Saturday afternoon.

Carlson had gone on the 10-day cruise with her other daughter and teenage grandson, who also claim to have fallen ill.

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She had seen medical staff, but was told she had probably brought a bug onto the ship with her, the daughter said.

D'Souza also claimed other cruise passengers had been locked out of their rooms on Monday without explanation.

The family believes the rooms were being disinfected.

"We'd like some answers," D'Souza told Sydney Morning Herald.

P&O has denied there was a gastro outbreak, and Queensland Police told Daily Mail Australia Carlson's cause of death was not being treated as suspicious.

"There is no reported gastro outbreak onboard," a P&O spokesperson told Daily Mail Australia.

"An elderly female passenger sadly passed away on Saturday on the Pacific Jewel cruise. Our thoughts are with her family."

Queensland Police determined the 79-year-old died of natural causes and are not treating her death as suspicious.

A report will be prepared for the coroner.