Australian health authorities are bracing for an outbreak of the swine flu which has killed more than 80 people in Mexico and is currently spreading throughout the world.

The new strain of swine flu has spread to the United States and Canada after killling more than 80 people in Mexico and there are also suspected cases in New Zealand, Europe, the Middle East and Asia.

This morning two people who recently travelled to Mexico were cleared of having the virus in New South Wales, but an Australian virologist is warning that it is "almost inevitable" that the virus will reach Australia.

With no cases yet confirmed in Australia, federal health authorities say they are ready to implement containment procedures at international borders if needed.

What concerns experts about this latest virus is that it is a combination of human, avian and swine strains, and that it passes so easily between humans.

Virologist Alan Hampson is regarded as one of Australia's top experts on influenza viruses.

"The virus is related to viruses that we've had in the human population since 1977, in terms of being the same sub-type of influenza A, so it's an H1 virus," he said.

"It's not dramatically different in the same way as the avian H5 influenza virus is.

"But clearly it is sufficiently different to be able to readily infect people and probably overcome existing immunity to existing H1 viruses."

Another virologist, Professor Ian Gust, says it is almost inevitable that the swine flu will reach Australia.

"I think it has the potential to spread throughout the world, that is to cause a pandemic. It's a novel strain that the majority of the population have no immunity to, and it clearly has the capacity to spread from person to person," he said.

The virus now appears to have crossed at least two oceans, with suspected cases turning up in the UK, France and New Zealand.

In New Zealand, tests are expected to show that schoolchildren picked up the virus while on a trip to Mexico.

The Greens want screening procedures put in place for arrivals at international airports, but Dr Hampson says this is not as easy as it sounds.

"It's very hard to screen for influenza coming into the country, because what we do know is that people can be infected and not show the signs of disease in the early stages, but can be spreading the disease now," he said.

Dr Ian Barr, from the World Health Organisation (WHO) Influenza Centre in Melbourne, says it is not yet the time to panic but that the outbreak is worrying.

And Dr Barr says it is unlikely any existing vaccines will be effective against this new strain.

"That remains to be seen," he said. "Authorities will be looking at that and testing, people here, from people who've been vaccinated with the current H1N strain, but it's likely that there'll be no or very little cross reaction, I suspect."

"In the initial reports from the US from the CDC [Centres for Disease and Prevention] ... their seven strains of their swine influenza are all susceptible to the influenza drugs such as Tamiflu and Relenza.

"They weren't susceptible to the older class of drugs, the adamantanes."

Australian health authorities say they are ready to implement containment procedures at the nation's borders to stop the spread of the virus.

Australia's chief medical officer, Jim Bishop, has written to hospital emergency departments and general practitioners to warn them about the virus and what symptoms to look for in patients.

And Professor Bishop is also urging anybody who has just returned from the US or Mexico to see their doctor.

The president of the Australian Medical Association, Rosanna Capolingua, says the new virus poses a serious risk.

However, she says the health system is well prepared to deal with it.

"There's certainly communication networks," Dr Capolingua said.

"There is a store of Tamiflu, the anti-viral agent, that's been kept in Australia as well.

"There's been suggestions of fever tents, how to decamp patients from primary care into isolation areas, how the hospitals would cope.

"There's been quite a lot of planning done in the past, and preparation for any of these sorts of circumstances."