Sydney  - Australians were warned against travel to Mexico Tuesday as doctors were monitoring the health of 20 people who returned from the Americas with flu-like symptoms.

Health Minister Nicola Roxon stressed that there had been no confirmed case of swine flu in Australia.

Roxon has ordered the captains of aircraft arriving from the Americas to report to quarantine officers any passengers they suspect of having influenza.

In Queensland, Premier Anna Bligh activated the state's pandemic plan after 12 people were checked for swine flu.

Queensland chief health officer Jeannette Young said she fully expected a case of the swine flu.

"That's why we're putting all this into place, that's why we are meeting planes that are coming from the affected areas and we're talking to them and assessing what's going on," Young told reporters in Brisbane. "Until we declare our first case in Australia, people can only bring it in from overseas." (dpa)