Shanghai dog owners rushed to license their pets over the weekend as the city imposed a new one-dog policy in response to the growing popularity of man's best friend, state media said Monday. Hundreds of citizens microchipped and vaccinated their pets as a new law took effect Sunday limiting households to a single canine in an effort to curb rampant barking, unscooped waste and the growing risk of dog attacks. To encourage more pet owners to license their dogs, the government of the commercial metropolis slashed the cost of the permits in the city centre to 500 yuan ($77) from the previous 2,000 yuan, the Shanghai Daily said. Residents who owned two or more licensed dogs before Sunday will be allowed to keep them but must maintain each dog's permit, state media reported. Dog ownership has grown alongside China's fast-expanding middle class with official estimates putting Shanghai's pet dog population at 800,000. Previous reports have said only a quarter of that number are registered. The city's human population was more than 19 million in 2009, according to the government. Many dog owners postponed obtaining new licences until the cheaper rate took effect, causing a spike in traffic at animal vaccination centres, the Shanghai Daily said. Animal rescue shelters have also been expanded in the expectation that many owners will abandon their dogs to avoid paying the licence fees, the report said. The government had previously said tighter regulation was needed to prevent adverse effects on the city's environment from noise, waste, and dog attacks. There were about 58 million pet dogs in 20 major Chinese cities at the end of 2009 and the figure is rising about 30 percent each year, according to a recent survey by Beijing-based magazine Dog Fans.