The spread of the virus has caused widespread panic, with hospitals and medical centres reporting rising demand for tests.

The national toll rose to 23 last night after two children who arrived in Sydney on a cruise ship and a nine-year-old boy who returned from a holiday in the United States tested positive.

Today that tally has been updated to 29 as AAP reports that four more people who arrived on a Qantas flight from Los Angeles to Sydney have tested positive to swine flu, and NSW health authorities are trying to contact other passengers from the flight.

The two five-year-old children were among 2000 passengers aboard the Pacific Dawn, all of whom are being asked to stay at home for seven days. Tamiflu was being arranged for the 130 who had flu-like symptoms when they disembarked.

According to the Federal Government's "health emergency" website, businesses that are not providing essential services should start planning how they could operate at a reduced level or even close down temporarily if need be.

In Melbourne, Mill Park Secondary College will be closed to students this week after a year 12 student became the second pupil diagnosed.

Health Minister Daniel Andrews said the 17-year-old boy was taken to hospital after playing football on Saturday. "He was immediately fitted with a face mask and admitted to an isolation room at the hospital," he said. He was later discharged.

The boy is the first person in the state to be admitted to hospital with swine flu, but a Department of Human Services spokesman said it was not worried about footballers that came into contact with him. "He's outdoors and it's not regarded in the same way as sitting in the class room for an extended period."

A statement on Mill Park Secondary College's website said staff were working with the department to identify students who had prolonged contact with the year 12 student so they could be given Tamiflu.

A teacher's aide from Thornbury High School also tested positive for the virus yesterday. The school has been shut down for the week because of two students with the virus.

Australian International Academy in Coburg North also confirmed an eight-year-old student with the virus yesterday, causing half the 600 students from the junior campus to voluntarily stay at home.

It emerged last night that Fremantle AFL players and officials were on a flight from Melbourne to Perth with a man who has since been diagnosed as the first case of swine flu in Western Australia.

Fremantle chief executive said 40 Dockers' players and staff who had been on the flight had been advised what course of action to take should they show symptoms.

As the flu continued to spread, hospitals and medical centres in the northern suburbs reported high demand from parents wanting their children to be tested for the H1N1 virus, including some without any flu-like symptoms.

Royal Children's Hospital director of emergency medicine Simon Young said about 550 children came to the hospital at the weekend, including some with flu-like symptoms.

But Dr Young said only a small minority were tested for swine flu. He recommended that parents worried about their children call their GP first.

Dr Nelum Soysa, a general practitioner in Coburg, said she tested a student from the Australian International Academy yesterday, but was disappointed to find out that she could not send the test to the Victorian DHS laboratory because the girl had no proven contact history with the eight-year-old infected at the school.

"I think the criteria for screening from the Department of Human Services is too tight … viruses don't wait to be told who to infect," she said.

For the up-to-date information call the influenza hotline on 180 2007 or nurse-on-call on 1300 60 60 24.

With NICK MILLER