Dog owners are being warned to be on their guard after the deaths of up to four dogs from suspected poisoning at Big Wave Bay in Shek O. The animals died within days of one another after displaying identical symptoms associated with poisoning from the highly toxic herbicide paraquat. It is commonly used as a weedkiller in Hong Kong but was banned in Europe in 2007. One owner found bones tinged greenish blue close to the area where the dogs lived and were walked, a veterinarian said, indicating a deliberate attempt to lure the animals using poison-laced bait. The bones were handed to the police, who are investigating. Veterinary surgeon Dr Chris Dixon, who treated two of the dogs, urged the government to ban paraquat, for which there is no antidote. "All the symptoms are associated with poisoning by paraquat, which is easily available in Hong Kong," Dixon said. "It's a cruel poison that causes a horrible death for wildlife, which is why it has been banned in Europe. "Long-term studies have also shown it poses health risks to agricultural workers and linked it to Parkinson's disease. There is no place for paraquat in Hong Kong." The police and the Agriculture, Fisheries and Conservation Department have confirmed the deaths of two dogs in Big Wave Bay on October 11 and 15. A police spokesman said the cases were classified as criminal damage and autopsies were being carried out. The Society for the Prevention of Cruelty to Animals said it knew of three suspicious deaths and one unconfirmed death in the neighbourhood. Dixon said he suspected the dogs were poisoned around October 5. He saw the first dog, a nine-year-old shih tzu cross breed, that day, and a year-old labradoodle a day later, he said. "The first dog's throat was burnt on the inside, which happens with this weedkiller," Dixon said. "The animal suffocates because [the herbicide] causes fibrosis of the lungs. It is a particularly nasty death." One woman said her two-year-old mongrel died six days after falling ill the same weekend as the three other dogs. She said it was the fourth dog she had lost as a result of suspected poisoning during her 13 years living in Big Wave Bay. "If a child was to pick up the bones, it could be very serious," she said. The SPCA executive director, Sandy Macalister, said dog owners must exercise caution in the area. "Keep an eye on your dog or keep them on a leash," she said. "If you suspect your animal has been poisoned, we would ask you to contact our hotline 2711 1000 immediately." The cases are not believed to be linked to the Bowen Road dog poisoner, who has killed about 200 dogs since 1989.