Almost 250 people were on the flight from Bangkok to Melbourne early this month with a 22-year-old student from Pakistan who was later diagnosed with the first case of polio in Australia in 20 years, officials said.

About 100 of the mostly-Australian passengers had been contacted and efforts were being made to get in touch with the others after a national health alert was issued on Friday.

"We will be running an immunisation session," said Victoria state's chief health officer John Carnie.

"For others, we will be doing it either through their general practitioner or whichever method is most convenient to the patient."

The student, who had been in Pakistan for four months before returning to Australia on Thai Airways flight TG999 from Bangkok on July 1, is in a Melbourne hospital after being admitted on July 7.

Mr Carnie said passengers on the flight were considered to be at low risk of contracting polio but it was a highly infectious disease and it was appropriate to take precautionary measures.

"The general public should not be concerned by this diagnosis as the chances of anyone else being affected are very low.

"When this student was taken ill, he remained at home, therefore limiting contact with anyone else."

His five flatmates have been quarantined and must return two negative test results for the virus over coming days before being released.

There is no cure for polio, which can cause permanent disability or death, but it has been largely eradicated by a comprehensive vaccine programme, with worldwide cases dropping from 350,000 in 1988 to 1,912 in 2006.

Polio remains endemic in just four countries – India, Nigeria, Pakistan and Afghanistan – according to the World Health Organisation.