Canada's top public-health doctor now recommends Canadians avoid travelling on all cruise ships to protect against the spread of the novel coronavirus.

Dr. Theresa Tam had previously advised Canadians to think twice about cruises but toughened her warning in a Monday morning news conference.

Tam says the ships may voyage to areas with confirmed or undiagnosed cases of the coronavirus and its associated respiratory disease, COVID-19.

There are six cases of the virus in Canada linked to a previous voyage of the Grand Princess cruise ship out of San Francisco.

Other Canadians, stuck on the ship's current voyage, are being brought back to quarantine in Ontario.

Ontario has reported another three caes of COVID-19, bringing the total in this province to 34.