S President Donald Trump and Canadian Prime Minister Justin Trudeau have agreed to close the US-Canada border to all non-essential travel in an attempt to curb the spread of coronavirus.
"We will be, by mutual consent, temporarily closing our Northern Border with Canada," Mr Trump tweeted.
He said trade would not be affected.
Both countries had already issued sweeping travel bans but had maintained exemptions for each other.
Canada relies on the US for approximately 75% of its exports.
The shutdown will affect tourists and shoppers, but goods will continue to be moved across the border.
Mr Trudeau had previously resisted closing the border to his country's most important trading partner.
"Nearly 200,000 people cross that border every day, and that border and that traffic that goes across that border is literally a lifeline for both the Canadians and the Americans on both sides of that border," Mr Trudeau's Deputy Prime Minister Chrystia Freeland said on Tuesday.
"We get our groceries thanks to truckers who drive back and forth across that border. Very urgently needed medical supplies and medicines go back and forth across that border. And essential workers go back and forth across that border every day."
Approximately $2bn in goods and services crosses the US-Canada border each day.
