Cheung Chung-chiu, director of training at the Canine Trainer Association Hong Kong, believes Antje may have escaped because it was bored, or she may be in heat and looking for a mate. In order to keep them in peak physical condition, bitches are not sterilised, an officer familiar with the police dog unit said.

'Heavy rain in the last few days might make it difficult for the dog to pick up the scent and find its way back home,' Cheung said.

Apart from wandering in areas it is familiar with, he suggested, the dog might be in a comfortable area such as on a hillside or around a reservoir.

Cheung said the police might need to raise the height of railings at their kennels as these dogs are extremely active and good jumpers.

A police spokesman said the force regularly reviewed measures at its kennels. There are 104 dogs in service and all are implanted with a microchip. The Belgian shepherd, also known as the Malinois, was introduced in 2002 and is expected to take over from the German shepherd as the main breed used by officers.

The Malinois is a little smaller than the German shepherd and is relatively long-lived, at about 13 years, meaning it offers at least 10 years of active service.

They are loyal and friendly, intelligent, highly obedient and easy to train. The Malinois is usually very healthy, resistant to disease and injury, and is agile and spirited.

The police use springer spaniels and labradors to search for explosives and drugs because they have a better sense of smell.