WATCH | Something is killing the dogs in Norway, but we don't know what

Dozens of dogs in Norway have recently been hit by a mysterious and at times fatal illness, raising concerns among dog owners who have been told to limit contacts between canines.

Some 200 dogs have displayed the same symptoms - bloody diarrhoea and vomit, intense fatigue - in recent weeks and around 25 of them have died, Norway's Veterinary Institute said Monday.

The number is an estimate, as the Scandinavian country does not have a national register.

"This doesn't necessarily mean that it's the same illness, as there are lots of illnesses that can lead to these kinds of symptoms in dogs," Veterinary Institute spokesman Asle Haukaas told AFP.

Autopsies on 10 dogs revealed in each case a severe intestinal infection and five of them had "abnormally elevated levels" of two bacteria, Clostridium perfringens and Providencia alcalifaciens.

The illness has been observed mostly in greater Oslo but there have been a few cases in other parts of the country.

Health authorities have urged owners to keep their dogs on a lead and to limit contacts between them. Many owners have stopped taking their pets to public areas and a number of dog shows and gatherings have been cancelled.

Several theories have circulated in social media, including the possibility of a virus, a bacteria, food poisoning, or intentional poisoning.

"What is a little strange with this illness is that it has struck quite a large number of otherwise healthy dogs in a short period of time and very swiftly," an official from Norway's food safety authority, Ann Margaret Grondahl, said.

The Veterinary Institute has ruled out salmonella, Campylobacteria and the possibility that the dogs may have ingested rat poisoning.

Dog owners have been urged to bring their pets to a veterinarian at the first sign of any symptoms.

There is nothing to indicate at this stage that the illness can be transmitted to humans.