The last time a major rat infestation was reported in Bukit Batok was late last year.

It involved the elimination of a rat enclave on a slope next to Bukit Batok MRT station.

The Straits Times reported on Dec 24 that about 200 rats had been killed by pest controllers.

The rats had thrived because of food left by stray dog lovers. This was verified by the Agri-Food and Veterinary Authority (AVA).

It told The Straits Times that from January to November, about 100 complaints had been lodged regarding stray dogs and people feeding them at Bukit Batok Central and its vicinity.

"While the feeding of stray animals is well intended, it becomes an offence when it causes littering of the environment," an AVA spokesman told The Straits Times.

In 2011, the National Environment Agency started a programme to monitor the rodent population in Singapore.

The agency discovered that in October and November last year, there were about 10,000 rat burrows across the island, an increase from 6,400 in the same period in 2013.

Some of the reasons given for the rise in numbers include food not being disposed of properly and construction activities that may have displaced rats from their nests.