More than two dozen passengers became ill with a stomach bug during a 14-hour Qantas flight from Chile to Australia on Thursday, with 16 taken by ambulance to a hospital on arrival at Sydney airport, officials said.

The 26 sick passengers were part of the same tour group and were suspected to have contracted their gastro intestinal illness before they boarded the flight in Santiago, Qantas said.

Network Ten television reported that the sick passengers were Australian high school students returning to their hometown of Melbourne after attending the Roman Catholic event World Youth Day in Brazil.

The Boeing 747 was met by ambulance paramedics who treated the sick passengers in quarantine.

Of the sick passengers, "16 patients required transport to hospital, three of whom were stretcher patients," New South Wales state Ambulance Service said in a statement. There were no further details of their conditions.

The New South Wales state Health Ministry said in a statement that the passengers developed vomiting and diarrhea consistent with norovirus infection, a common cause of outbreaks of gastroenteritis in Australia and elsewhere.

Qantas spokesman Luke Enright could not say when the flight crew became aware of the sickness on board. It was not an emergency that could have resulted in the flight being diverted, he said.

"They've known for some time in the air that sickness was aboard so they were able to call through and organize for the appropriate authorities to greet the aircraft at the arrival, and those passengers were quarantined," Enright said.

The ill passengers were moved to seats at the rear of the plane near where four toilets were located, Australian Associated Press reported. Enright confirmed that the passengers were seated near the rear, but could not say whether they had been moved there by the cabin crew.

Qantas said other passengers were advised to keep a close eye on their health over the next two days and to seek medical advice if they feel ill.

Enright declined to say how many passengers were on the flight. AAP reported that more than 300 passengers were aboard, without citing a source.