US 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.
We will be, by mutual consent, temporarily closing our Northern Border with Canada to non-essential traffic. Trade will not be affected. Details to follow!
— Donald J. Trump (@realDonaldTrump) March 18, 2020
End of Twitter post by @realDonaldTrump
The two leaders had spoken on Wednesday to discuss the changes, Mr Trudeau said.
"I want to be clear though that essential travel will still continue," he said at a press conference.
"No matter who you are or what you do, this is a time when you should be focused on your health and that of your neighbours. Not: are you going to lose your job, are you going to run out of money for food or medications."
What is in the agreement?
Details of the final deal have yet to be released in writing but both leaders have stressed that cross-border trade will not be blocked.
Supply chains must be preserved so trucking would not be affected, Mr Trudeau said.
"That is something we remain committed to," he added.
Approximately $2bn in goods and services crosses the US-Canada border each day.
Canadians who needed to travel for other "urgent reasons" would also not be impacted, Mr Trudeau said.
There is no set timeframe for how long the border closure will last.
What prompted the ban?
Mr Trudeau's government 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," 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."
But both leaders had kept the notion of travel restrictions on the table, as both countries have struggled to halt outbreaks of Covid-19.
Earlier this week, Mr Trump warned against discretionary travel and said that "we have very strong emergency powers when it comes to something like this, both on the southern and the northern borders".