Japan will ban the entry of all foreign visitors starting Tuesday, as omicron, the new variant of COVID-19, continues to spread around the world, Prime Minister Fumio Kishida announced Monday. 

The news comes after Japan announced over the weekend that anyone arriving from South Africa and eight other countries had to quarantine for 10 days at a government-designated facility.

Two cases of the new variant omicron have been confirmed in Ontario, Canada, government officials announced Sunday.

"Today, the province of Ontario has confirmed two cases of the Omicron variant of COVID-19 in Ottawa, both of which were reported in individuals with recent travel from Nigeria. Ottawa Public Health is conducting case and contact management and the patients are in isolation," Christine Elliott, deputy premier and minister of health, and Dr. Kieran Moore, chief medical officer of health, said in a statement.

South Africa's President Cyril Ramaphosa addressed his nation on Sunday following the detection of the omicron COVID variant and said the country's National Coronavirus Command Council met Saturday to consider the recent rise in infections and the possible impact of the omicron variant. They have decided not to impose further restrictions at this stage.

"We considered the fact that when we encountered previous waves of infection, vaccines were not widely available and far fewer people were vaccinated," Ramaphosa said.

Ramaphosa said they will closely monitor infection rates and hospitalization over the coming days and will review the situation in another week.

Only 23.66% of South Africa's population is fully vaccinated against COVID, according to the Africa CDC.

President Joe Biden, who is returning to the White House Sunday afternoon, will be briefed in person by his COVID-19 response team and Dr. Anthony Fauci for an update on the omicron variant.

This is Biden's third briefing on omicron since Friday.

"This afternoon, the president will have an in-person briefing with members of his COVID-19 response team and Chief Medical Advisor to the President Dr. Fauci to provide an update on the omicron variant and the administration’s response," a White House official told ABC News.

-ABC News' Justin Gomez

The United Kingdom announced Thursday new travel restrictions for six countries over concerns about a new variant of the novel coronavirus that emerged in South Africa. 

The variant, known as B.1.1.529, has also been found in Botswana and Hong Kong in travelers from southern Africa. It has not yet been detected in the U.K., officials said.

"The early indications we have of this variant is that it may be more transmissible than the delta variant, and the vaccines that we currently have may be less effective against it," U.K. Health Secretary Sajid Javid said during a briefing Thursday.

Starting midday on Friday, all flights from six southern African countries -- South Africa, Namibia, Lesotho, Eswatini, Zimbabwe and Botswana -- will be temporarily suspended, and travelers entering the U.K. from those countries after 4 a.m. on Sunday must quarantine in a government-approved hotel for 10 days.

Currently, B.1.1.529 is not designated by the World Health Organization as a variant "of concern" or "of interest." So far, 22 cases have been confirmed in South Africa, according to the country's National Institute for Communicable Diseases.

The WHO's technical working group is scheduled to meet Friday to assess the new variant and may decide whether to give it a name from the Greek alphabet, based on its naming system for variants of concern and variants of interest.

The virus evolves as it spreads and many new variants, including those with worrying mutations, often just die out. Scientists monitor for possible changes that could be more transmissible or deadly, but sorting out whether new variants will have a public health impact can take time.

-ABC News' Rashid Haddou-Riffi