Australia now has recorded 29 confirmed cases of human swine flu influenza A (H1N1) as of Tuesday morning.

On Monday, test results for a nine-year-old boy who arrived in Sydney on flight QF12 from Los Angeles on Sunday returned positive for swine flu.

NSW Health said on Tuesday further testing had found that three members of the boy's family had now tested positive for human swine flu as well as a fourth, unrelated, passenger who has also tested positive.

"The flight was Qantas flight 12 (QF12) from Los Angeles to Sydney," NSW chief health officer Kerry Chant said in a statement.

"The boy and his family had been travelling throughout the USA and Canada.

"These family members have been assessed by public health officials, and have been instructed to remain in home isolation."

Ms Chant said NSW Health had contacted 21 people who were seated near the boy and his family.

"These people will be provided with Tamiflu and are now in home isolation until Monday," she said.

"NSW Health are also now proceeding to contact passengers who were seated next to the additional passenger.

"We want to ensure that passengers on flight QF12 are aware that five passengers on that flight are now positive and want to ensure they take all necessary precautions."

The development follows the positive test results of two children on board the Pacific Dawn cruise ship that arrived in Sydney on Monday.

Their testing delayed the departure of the vessel on its next cruise by seven hours, and 130 other passengers were quarantined with symptoms of respiratory illness.

The remaining 1,800 disembarking passengers were asked to stay at home or in their hotels for up to seven days.

The ship eventually set sail with its new passengers and a fresh crew on Monday night.