The number of dengue cases in a week has hit a 31/2-year high, with 666 cases recorded from July 7 to 13, the National Environment Agency (NEA) said.

In an update on its website on Monday, NEA said that this figure was 73 more than the previous week. It also surpassed the previous weekly peak of 637 cases, recorded in January 2016. As of Sunday, there were a total of 7,374 dengue cases this year, about five times more than the 1,481 cases seen in the same period last year.

"Urgent action is needed to eliminate potential mosquito breeding habitats in the community," NEA said.

Of the current 182 dengue clusters, the largest cluster is located in the areas around Woodlands Avenue 6, Woodlands Circle, Woodlands Drive 40, Woodlands Drive 60, Woodlands Drive 70 and Woodlands Drive 72. There were a total of 216 cases reported here.

However, NEA noted that there has been a "slowing down" in transmission of the virus in this cluster in the past seven weeks. There was a case reported in the past two weeks, compared with 27 cases in a week when the transmission was at its peak.

Across Singapore, large clusters with a relatively fast rate of dengue transmission have been observed in Pasir Ris, Joo Chiat and Jurong East, NEA added.

There are now 48 high-risk areas with 10 or more cases, such as in Bedok, Choa Chu Kang, Tampines, Chai Chee and Pasir Ris.

Already, 44 people have had the more severe dengue haemorrhagic fever this year, and five people have died.

During the warmer months between June and October, "a national collective effort is critical to prevent dengue cases from rising further", the agency said.