Fluffy or short-haired, gentle or fierce, Beijing's dogs are being targeted by cage-wielding police, but one officer is secretly trying to ensure the campaign's bark is worse than its bite.

A stepped-up crackdown on "oversized" and unregistered dogs has provoked panic among the capital's expanding ranks of pet owners, and enraged China's emerging animal rights movement.

The most subversive response of all has come from one uniformed crusader, a policeman himself, who has defied the rules to rescue dozens of pooches from the clutches of his fellow officers over the years.

"My colleagues don't have any feelings towards dogs," said the 50-year old, asking to be identified only via his online nickname, Xiao Hei.

In a small guardhouse office where he keeps seven canines, he reluctantly admitted that his actions were against the law, nodding his head when asked.

"I ask my colleagues [at the police station] first. But if they won't give the dog to me, I'll steal it," he told AFP, a black spotted dog nestling against his blue police shirt.

His modus operandi is simple -- he returns to his police station late at night, when fewer personnel are on duty, takes a dog out of its cage, and sneaks it past his fellow officers.

He tries to find his charges new homes online, where activists have lionised him as Beijing's greatest dog-lover.

Xiao Hei said he was spurred to action by the sight of animals packed into cages waiting to die. "I felt terrible when I saw them," he said. "I have no choice."

Beijing banned all canines from its city centre until 1983, but some estimate it is now home to more than a million dogs, as well as hundreds of veterinary clinics, dog hair salons and a luxury pet park with a bone-shaped swimming pool.

But the city has maintained a ban on 40 large breeds, from St. Bernards and Great Danes to British bulldogs and dalmatians, according to regulations posted online.

Registration of smaller dogs -- costing 1,000 yuan ($160) -- is compulsory, with annual renewals priced at 500 yuan.

"Some owners don't have the ability to pay," said Xiao Hei, pointing at a small golden creature. "This one was taken from an old person living on social security."

A police order in June gave owners of large dogs 10 days to remove their pets from central Beijing or face being fined 10,000 yuan ($1,600) and having their animals seized.

Authorities say the campaign is aimed at ridding the city of dangerous breeds liable to target humans. State-run news agency Xinhua reported that 2,400 dog attacks occurred in China last year.

Once oversized dogs are confiscated they cannot be retrieved. The animals are put down and sometimes sold to restaurants for their meat, activists say.

A video showing a policeman grabbing a small white dog from the arms of its angry owner before placing it in a cage went viral in June, with outraged supporters venting their fury online.

"Never give your dog to the police -- it's a road to death," one user posted on Sina Weibo, a social networking service similar to Twitter.

"If you want to be a dog, or a person, it's best not to be born in China," wrote another.

Police have not announced how many dogs have been seized in this year's campaign.

But Liu Xiaoyi, who owns a Beijing dog shelter, said: "It's bigger than previous years."

Panicked dog owners have placed pooches in temporary kennels outside city limits until the campaign dies down, she said, while others have taken to walking their pets late at night when patrols have finished.

"We only dare to walk our dog after 12 at night, when the police are sleeping," said bank worker Hai Tao. "One person keeps lookout while the other walks the dog."

A Beijing financier surnamed Zhang, who walked two golden retrievers past white apartment blocks on a moonlit night, said the regulations were unjust.

"Just because a dog is big, that doesn't mean its aggressive," he added.

Pet ownership has ballooned across China, with more than 30 million households now keeping a cat or dog, according to research group Euromonitor.

The growth has been accompanied by increased activism, with volunteers banding together to mount rescues of dogs and cats from trucks transporting them to restaurants where they are served as meat -- evidence of a growing animal rights movement in the country which has no laws against animal cruelty.

Xiao Hei says he has rescued 12 dogs so far this summer -- five of which he keeps at home, to the consternation of his wife, he said, and in defiance of regulations limiting households to one canine each.

"The regulations are unreasonable," he said bluntly, in an unusual public expression of dissent by a law enforcement agent.

"If people can afford to raise more than one dog, I don't see why it should be illegal."