Health Minister Gan Kim Yong on Friday warned against complacency and failure to have contingency plans for possible future pandemics.

The cost could be considerable, he noted.

Quoting World Bank estimates, he said a severe flu pandemic could cost the world $3 trillion, or a 5 per cent drop in global gross domestic product.

When Sars hit Singapore in 2003, visitor arrivals fell 67 per cent in a month and hotel occupancy dropped from 75 per cent to a low of 20 per cent, he said.

Speaking at the National Security Conference at the Pan Pacific Hotel, Mr Gan said: "We cannot afford to become complacent.

"In our highly globalised world, where cities like Singapore are well connected by air travel, the risks of imported cases and subsequent transmission of infectious diseases within the population remain ever present."