The Agri-Food and Veterinary Authority (AVA) is looking into allegations that 18 community cats have been removed from St John's Island.
In a statement to The Straits Times yesterday, the authority also urged members of the public with information on the cats to come forward.
The cats' apparent disappearance is understood to have taken place about a week ago on Aug 26, said Ms Angela Ling, who set up the Facebook page St John's Island's Cats and is a regular caretaker of the cats.
Ms Ling, 41, has been taking care of the stray cats on the island since 2014. She told The Straits Times that a follower of the cats' Facebook page who had been fishing on the island told her that she saw a group of people armed with 18 carriers take the cats away.
They told the Facebook group follower that they were taking the cats to the mainland for treatment.
But four of these cats were found yesterday, abandoned near Sembawang beach.
Ms Ling, who works in the service industry, was informed about three of the abandoned felines through a private message and recognised them when shown pictures of the cats.
She found one more cat after she rushed to the scene.
Of course I'm very worried about the missing cats. I'm choosing to believe that whoever took them had good intentions. I just want to know that the cats are okay.
MS ANGELA LING, a regular caretaker of the St John's Island cats.
Aside from the four cats, the remaining 14 are unaccounted for.
Ms Ling said that the four cats she found showed some signs of dehydration.
One appeared to be suffering from a gum issue and "clearly wasn't well taken care of in the week it went missing", she said.
"These cats are very old strays so even if the people who took them have good intentions and want to rehome the cats, it's very difficult to find people willing to adopt the cats," she added.
She reported the missing cats to the AVA and plans to make a police report as well.
St John's Island used to have some 100 cats, Ms Ling said. Many domestic cats born on the island were left behind when former residents of the island moved out.
Ms Ling visits the island about once every two weeks. She helps to appeal for cat food for the felines and has engaged workers on the island to help with feeding them. She also takes the cats to veterinarians when they need medical treatment.
On the disappearance of the cats she has cared for over the past four years, she said: "Of course I'm very worried about the missing cats. I'm choosing to believe that whoever took them had good intentions. I just want to know that the cats are okay."