Four dogs have reportedly died within 24 hours from "what appears to be ingesting rat poison" in Swansea.
It is believed that three of the dogs came into contact with the poison in Clyne Gardens and another near the Loughor estuary.
One man, who runs a dog walking business in the area, said he spoke to two of the owners and they said a vet confirmed their dogs had died from eating rat poison.
South Wales Police have warned owners to be vigilant when out walking their pets.
David Goldsmith, who is joint owner of a pet sitting and dog walking business, said he first heard about the incidences from different dog walking groups. He then spoke to two of the owners whose dogs had died.
The owners told me that it was confirmed by their vets that it was rat poison. To begin with it was three dogs in Clyne Park but 12 hours later a dog passed away after going near the Loughor estuary.
He added that they usually walk their dogs in the two areas where it is believed the rat poison was ingested.
Swansea Council confirmed that pest control had not been involved in any distribution of rat poison in the two locations.
South Wales Police has also warned dog walkers in the area to be vigilant while out with their pets.
A spokesman for the force said: "Police in Swansea were called on Saturday, February 15, concerning reports that several dogs had died from what appears to be ingesting rat poison in the Clyne Park and Loughor estuary area.
"Dog walkers should be vigilant when walking their pets in the area and to report specific concerns to the RSPCA or the local authority."
A spokeswoman for the RSPCA said these reports were "deeply distressing" and urged people to contact their 24-hour advice and cruelty line on 0300 1234 999 if they have concerns.
In November 2018, another dog was said to have died while others were ill after suspected poisonings in Clyne Gardens.
Signs and symptoms of poisoning include your pet vomiting, appearing depressed, sleepy, drunk or uncoordinated, seizures and breathing difficulties.