Photographer Mr Leung, who owns several mastiff dogs at the home he shares with his girlfriend in Tong Sheung Tseun, Tai Po, said there were no more than 10 dogs of the same breed and class as Anna in the whole of Asia.

Fellow dog lovers had put her value at about $700,000, Mr Leung said.

The thieves struck at 11.45am as Mr Leung was walking another of his mastiff dogs, Capone, whom he described as Anna's boyfriend, in the village.

He left Anna tied to the gate of his home while his girlfriend slept indoors. As he walked to a cafe in the village with Capone, his girlfriend woke to hear the dogs barking furiously.

When she ran outside, Anna had been stolen. Neighbours said they saw two men grab the dog, leash her and bundle her into a white goods van.

Mr Leung said he suspected the theft had been carried out by someone with an inside knowledge of dog breeding.

'I feel very sad about losing Anna, as it's very difficult to breed these dogs. But I'm sure I will find her,' he said.

'Her boyfriend, Capone, is very upset. I hope police and the press can help us inform the public and hopefully Anna will come back soon.'

He said Anna was not insured as it was not possible to get insurance cover for such pets in Hong Kong.

Anna weighs 59kg and is a metre tall.

She belongs to the southern Italian species of Mastino Napoletano, which Mr Leung said was a guard dog with a less aggressive temperament than others in the mastiff breed.

She was born using artificial insemination, which cost about $20,000.

Mr Leung bought Anna together with her mother, Margherita, in Germany last July. Anna's father, Mose, was the champion of an international dog show in 1985 and her grandfather, Sasone, was a champion in 1981.

Mr Leung said some buyers in the United States and some in Hong Kong had already booked to buy the offspring of Anna and Capone at US$3,500 (HK$27,300) each.

Police officers said the two thieves may have found out about Anna through pet magazines or dog shows and come ready with a leash and getaway van.

Mr Leung said it would be difficult for the thieves to sell Anna on as a pedigree as she was implanted with microchips and had a tattoo on one thigh.

'We suspect she might have been stolen for mating and the thieves expect to make money by selling her offspring,' Mr Leung said.

There are about 6,000 Neapolitan mastiffs in the United States and the increasingly popular breed is growing in number at the rate of 25 per cent a year, but Anna is rare and highly valuable because of the purity of her breeding, Mr Leung said.