Governments and health authorities worldwide went on the alert over the weekend for a possible influenza pandemic as the death toll from a new strain of swine flu in Mexico reached 81.

Janet Napolitano, homeland security secretary, on Sunday declared a "public health emergency" in the US as about 20 people there were confirmed to have been infected, though none is seriously ill. The World Health Organisation in Geneva had earlier made a similar announcement.

The World Bank on Sunday agreed to Mexico's request to release emergency credit of more than $200m (£136m) to fund its swine flu programmes.

Keiji Fukuda, the WHO's assistant director-general for health security, said its emergency committee would decide on Tuesday whether to raise the official pandemic threat level above "phase three", where it has been for several years in response to a different virus – H5N1 bird flu in Asia.