Dengue numbers have risen for the fourth straight week, with 459 people diagnosed with the viral infection last week, up from 429 the week earlier.
More than 6,600 people have been infected this year. One has died.
There are now more than 50 active clusters, primarily in the eastern and southern parts of the country.
The biggest cluster, with 183 people infected, is in the Farrer Road-Holland Road area, with at least 130 workers at the Leedon Residence construction site.
The Lorong Lew Lian-Serangoon Central area, with 119 cases, is the next biggest cluster; followed by Hougang Avenue 11-Lorong Ah Soo, with 110 cases; Flora Drive, with 86, and Hougang Avenue 3-Street 22, with 34 cases.
There are another seven clusters with more than 10 cases each that have been red-flagged.
A cluster is formed when at least two people living or working within 150m of each other have dengue within a two-week period.
Singapore had its worst dengue epidemic last year, when more than 22,170 people came down with the disease that sent hundreds to hospital and killed seven people.
This time last year, 8,453 people had been infected.
People with dengue often suffer from high fever, head, eye, muscle and bone ache and might suffer a rash. In more severe cases, they might bleed in the gums and internally.
The National Environment Agency (NEA) warned on its dengue website that June to October is the period when dengue normally peaks in Singapore.
These are the hotter months, when the Aedes mosquito, which spreads the disease, breeds more frequently and when the insects also mature faster.
Although the main virus in circulation remains Den-1, which was the cause of last year's epidemic, it said that many in the population still lack immunity.
There are four dengue strains. People who have been infected are protected against only that strain.
Over the years, all four strains have been active.
NEA said in the past week, it has issued three stop-work orders to construction sites found breeding mosquitoes and will prosecute recalcitrant contractors in court.