Canada has surpassed a grim milestone, recording its 30,000th COVID-19 death since the pandemic began in early 2020.

Ontario reported nine additional deaths attributed to the virus on Thursday, pushing Canada's overall total to more than 30,000 as experts warned of fresh threats posed by the more transmissible Omicron variant.

Canada reached 10,000 COVID-19 deaths last November, and surpassed 20,000 deaths two months later in January, 2021 — a leap that occurred before enough vaccines were administered to have an impact.

Experts say vaccines have significantly limited the number of people dying from the virus daily since then, with some estimates suggesting between 75 per cent and 90 per cent fewer deaths in each age group, compared to what would normally be expected.

Canada's chief public health officer Dr. Theresa Tam says the arrival of vaccines a year ago resulted in a "dramatic shift" in Canada's COVID-19 trajectory, with a particular drop in mortality rates.

Tam has said mortality rates continue to be "sustained at a lower level" but warned of rising infection rates due to the more transmissible Omicron variant.