Preliminary testing has confirmed the presence of the strain on a turkey farm in Abbotsford and a broiler breeder farm in Chilliwack, with both sites now under quarantine to try and guard against disease spread.
In addition to these sites, two additional farms in Fraser Valley are also under quarantine as they received birds from one of the original farms and so were determined to be at high risk. Birds on these farms are also showing signs of illness, according to the Canadian Food Inspection Agency (CFIA).
It has warned the poultry sector of the need to step up biosecurity measures and is carrying out further tests to determine the pathogenicity as well as the precise subtype and strain of the virus, with results expected in the coming days.
Initial tests were carried out on Monday 1 December after the original two operations reported sudden deaths of birds last weekend.
All susceptible birds are to be culled and a surveillance zone set up around the effected locations.
The CFIA said it was working closely with the Province of British Columbia, the owners of the two farms and the poultry industry to manage the situation.
The World Organisation for Animal Health (OIE) has recommended that animal disease surveillance is strengthened worldwide following the recent spread of HPAI H5N8 in Europe and Asia.
It said that millions of birds had already fallen victim to H5N8 in the past 11 months alone, and although outbreaks have so far been rapidly controlled by sanitary authorities, "there are important repercussions for the poultry sector".
According to the OIE, while the globalisation of animal trade has increased the possibilities for pathogens to be spread from one side of the world to the other, "a simple natural phenomenon, such as migratory movements of wild birds, can also cause the worldwide dissemination of a disease".
Dr Vallat, director general, OIE, said: "The crises of the past 20 years, such as those related to avian influenza H5N1 and H7N9, foot-and-mouth disease and mad cow disease, and now Ebola, show us that while it is true that the policies of combating diseases at their animal source are an expense for the budgets of individual states or the international community, the amount is derisory compared to the costs involved in dealing with a panzootic or a pandemic."