Prime Minister Justin Trudeau says "rare exceptions" to new travel restrictions will be made on compassionate grounds, but that more contagious COVID-19 variants now taking hold in Canada mean tough rules must be implemented in the next few weeks.

Trudeau announced last week that passengers returning from abroad will have to quarantine at a hotel for up to three days after taking a PCR test at the airport, but no date has been set for when this will take effect.

The move is one of several measures meant to choke off entry of the virus into Canada, but comes after case numbers of more transmissible variants have begun to rise.

Chief public health officer Dr. Theresa Tam says 148 cases of the variants that first emerged in the United Kingdom and South Africa have been confirmed across the country, even as overall case counts continue to decline.

Health authorities in Ontario, Alberta and British Columbia have identified both mutations, with Ontario's single confirmed case of the variant that first emerged in South Africa found in a Peel Region patient who had no known contact with travellers, raising fears of community spread.

The Public Health Agency of Canada says foreigners can still apply to enter the country for non-essential reasons that include supporting a critically ill person, attending a funeral or being with a loved one who is dying.