Canada closed its borders to all foreign nationals except US citizens and permanent residents on March 16, with Prime Minister Justin Trudeau urging people to limit social contact to stem the spread of the new coronavirus.
Several other countries have taken the same step. The 27-nation European Union proposed shutting its external borders for 30 days on March 16.
"We will be denying entry into Canada to people who are not Canadian citizens or permanent residents ... it is a significant step that we take in exceptional circumstances," Trudeau told reporters outside his home, where he is under quarantine after his wife, Sophie, tested positive for the respiratory virus.
As the virus' spread accelerates in Canada, Trudeau urged people to stay home and restrict contact with others.
"Staying home is an important step to protect the community and each other. We all have to do it," he said.
Theresa Tam, Canada's chief public health officer, said that the next two weeks were crucial in trying to stem the outbreak.
The death toll in Canada rose to four on March 16. The number of infected jumped to 407 from the 341 reported at 9am (1300 GMT) earlier in the day, medical officials said.
The new deaths occurred in the same nursing home in the Pacific province of British Columbia, which is directly north of Washington, one of the worst-hit US states.
Trade will not be affected by the border closing. Canada shares a long unguarded frontier with the United States, which takes 75% of Canadian goods exports.
Asked why US citizens were exempt, Trudeau said the close bilateral integration meant the United States was in a different category from other nations. But he added that more measures could be announced soon.
"Both countries rely on each other to provide essential goods ... so it's very important we do this with a degree of precision and in the spirit of a strong relationship," Health Minister Patty Hajdu later told reporters.
British Columbia said, however, it was concerned that US citizens would be allowed in.
"Our strong message (is) that visitors from the United States not come to British Columbia," said provincial Health Minister Adrian Dix.
The border closure helped drive down Air Canada's stock by as much as 38%.
Canada will reroute all international flight arrivals to four airports - Toronto, Calgary, Montreal and Vancouver - and has imposed tougher screening.
Weddings, Baptisms on Hold?
The country's main stock market index tumbled nearly 10% and the Canadian dollar hit a four-year low.
Ontario, the most-populous province, and one that accounts for nearly half of confirmed cases, said it would delay a March 25 budget and instead deliver an economic and fiscal update.
Toronto, Canada's largest city, recommended that bars and restaurants stop in-person service and that theaters close.
Quebec on Monday recommended the suspension of all religious functions, including baptisms, weddings and funerals. For any funerals that proceed, the number of mourners should be reduced, the province said, without specifying how many.
"If it's possible for you to express your caring to the family, do it by internet, or by phone," Public Health Director Horatio Arruda said.
Trudeau, who has promised to unveil a major stimulus package soon, said that "in the medium term and then into the long term, we will need to invest significant amounts to restore people's confidence in the economy."