Dengue fever infections are mounting alarmingly in Singapore due to a change to a more deadly strain of the disease, sparking fears of the city-state's potentially worst epidemic yet, news reports said Tuesday.

Unless the trend of infections is halted, health officials warn that the number of sick people could hit record levels within three years.

The number of infections from January through March is already 60 per cent higher than during the first quarter of 2007, said figures published in The Straits Times.

"If nothing is done to stop the spread, the number of cases will increase very significantly," Dr Ng Lee Ching, head of the Environmental Health Institute, was quoted as saying.

The severe, flu-like illness is showing up in a more deadly form, called dengue haemorrhagic fever, for which there is no vaccine or cure, Ng said. Victims can only be treated for the symptoms, which include high fever, body aches and nausea.

Twenty people died from it last year.

Experts are further concerned because the Aedes mosquito, which spreads the disease, appears to be moving into areas where it previously was not found.

The city-state is spending 200,000 Singapore dollars (145,000 US dollars) a day in a massive effort to destroy breeding sites and a targeted war against mosquitoes in areas where two or more people fall ill.

Last year, more than 5,000 homeowners were fined 200 Singapore dollars (145 US dollars) for allowing mosquitoes to breed. Construction sites found with the insect pests breeding are fined 2,000 Singapore dollars (1,459 US dollars).

"We cannot understand why the numbers are climbing," Ng said.