Gastro bug cripples hundreds on Sydney bound cruise ship

A gastro outbreak on-board a Sydney bound cruise ship has left 158 passengers sick.

Passengers on the 12-day New Zealand cruise departed the Diamond Princess this morning at Sydney's International Passenger Terminal after the outbreak occurred at sea.

The ship’s captain reportedly came over the ship’s loudspeaker and advised sick passengers to stay in their rooms.

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Passenger Stephen Dinale, from Sydney told Fairfax Media it was like being on the 'voyage of the damned' with people vomiting in the swimming pool and throughout the ship.

"You would be (in) the elevator and I would be hitting the button with my knuckle and other people would be running down the corridor holding their mouths," he said.

Mr Dinale was one of about 4000 people on board the ship.

The ship’s pool was drained empty as a precaution.

“We were told that some people hadn’t reported it for about four days,” one passenger told 9NEWS.

“So other people caught it.”

South Eastern Sydney Local Health District said the passengers and a small number of crew had come down with a bug and were attended to by the ship's doctor.

The outbreak has been contained, with about 35 passengers still affected by the gastro bug when the ship docked in Sydney, Princess Cruises said in a statement.