Monkeys at a playground and the bottom of a housing block in Sunset Way Residence in Clementi Street 13 on Wednesday.
Long-tailed macaques have recently been appearing in neighbourhoods such as Clementi and Punggol, with some even entering homes.
Experts say the feeding of these animals can cause them to see residential spaces as food places, leading to assertive behaviour.
The macaques usually live and look for food at the edge of the forest. But they could end up moving when new developments affect their home bases, to go forage in nearby residential areas.
Officers from the National Parks Board are working to keep the animals away through monkey guarding. When monkeys approach, trained personnel will make loud noises, such as hitting a stick against a railing.
The monkeys consider loud noises unpleasant, and when they are conditioned to relate residential areas with such noise, they will keep away.