The United States' border with Canada will be closed to nonessential travel beginning Saturday, Secretary of State Mike Pompeo said at a Friday press briefing. The border closure will be reviewed after 30 days, Pompeo said.

The announcement comes two days after President Donald Trump and Canadian Prime Minister Justin Trudeau mutually agreed to close the border to help contain the spread of coronavirus.

"We will be, by mutual consent, temporarily closing our Northern Border with Canada to non-essential traffic. Trade will not be affected," Trump tweeted Wednesday.

"I just spoke to President Trump again this morning and we have agreed that both Canada and the United States will temporarily restrict all nonessential travel across the Canada-U.S. border," Canadian Prime Minister Justin Trudeau said in a news conference on Wednesday morning.

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Trudeau, who is in the midst of a 14-day self-quarantine after wife Sophie Grégoire Trudeau tested positive for coronavirus, also stressed that "essential travel" won't stop. "Our governments recognize that it is critical we preserve supply chains between both countries," Trudeau said. These supply chains include the passage of food, fuel and medicines reach people in both countries. Trucking won't be affected, for example.

U.S. flights headed to Canada will continue as scheduled, though passengers will face screening, according to the U.S. State Department. Those arriving must self-isolate for 14 days, and anyone exhibiting symptoms won't be allowed to enter Canada.

But travelers won't be permitted to cross the border for recreation and tourism, Trudeau explained.

Processing thousands of people per day puts border agents at increased risk for contracting COVID-19 and passing it along to others.

CBP employees have been permitted to use protective equipment, such as masks, in appropriate circumstances.

Both the U.S. and Canada border agencies have reported increasing their questions at entry about international travel and health to spot ill travelers during the spread of the coronavirus.

Canada's border agency has been updating its Twitter account with steps it is taking during the pandemic as well as information on mitigating the spread of the virus.

Why is the border closure happening now?

"We took major measures on Monday to close off our borders to international travelers, and we took two days to coordinate this further measure with the United States to ensure that we do it properly and in cooperation with each other," Trudeau said. Canadian Deputy Prime Minister Chrystia Freeland called Pence on Tuesday for the purpose of beginning discussions, and they were able to make the announcement Wednesday.

Extra travel right now, based on government guidance, could be a hindrance to stopping the spread of the virus. In both the U.S. and Canada, people are encouraged to to stay home.

"This collaborative and reciprocal measure is an extension of that prudent approach," Trudeau said.

However, essential travel and trade is still being allowed because of health and economic safety.

"The fact is we are working very closely with the United States at this time to introduce specific rules that will keep both Canadians and Americans safe," Trudeau said. It's important for the border to remain open, considering the $2 billion worth of goods that cross it each day. It's critical for health of economy and citizens.

When will the US-Canada border reopen?

The closure is initially set to last 30 days but that period could be extended depending on the progress of the virus

"These measures will last in place as long as we feel that they need to last," Trudeau said, adding that Canada and the U.S. will closely coordinate.