SYDNEY - Australian authorities said Tuesday they were investigating 70 possible cases of swine flu and cautioned against travel to Mexico, as the World Health Organisation (WHO) warned of a possible pandemic.

Prime Minister Kevin Rudd vowed to devote "all necessary resources" to the evolving flu threat, as possible cases of the disease more than doubled, covering all but one of the country's states and territories.

Health Minister Nicola Roxon said it was "at least possible, if not likely" that cases of the virus would be confirmed in coming days, and Australia's health officials were on high alert.

Mexico, the epicentre of the outbreak, said the number of confirmed and suspected deaths from the flu had risen to 152, while some 1,600 people were thought to be infected there.

The number of confirmed cases in the United States more than doubled to 44 and Britain and Spain both said they had registered patients sick with swine flu, the first cases in Europe.

In Australia, five people, including children, had tested positive for a type A virus -- to which swine flu belongs -- in the state of New South Wales, and Roxon said they would undergo further tests.

A further 65 possible cases were spread across the rest of the country, including two women who fell ill during a flight from Los Angeles to Brisbane.

They have been sent home with Tamiflu, an anti-viral drug, while awaiting the results of swine flu tests, officials said.

"This evening the figure is 70, that's the most up-to-date information," a health spokeswoman told AFP late Tuesday.

"But that is a constantly evolving figure as people are cleared," she said.

Many of the sick had been in Mexico or the United States in the days before their travel and were being urged to remain in isolation until they had been cleared.

The foreign affairs department raised its travel warning for Mexico, advising Australians to reconsider their need to visit, and urged those already in the country to consider leaving.

Roxon said clinical staff had been stationed at all Australia's international airports, while all airlines operating from the Americas were required to report the health status of passengers before landing.

The WHO raised its flu pandemic alert level from three to four overnight, but said a pandemic was "not considered inevitable at this time".

- AFP/ir