Canada and the United States are preparing to extend the closure of their border to non-essential travel because of the coronavirus pandemic until August 21, a source familiar with the talks said Tuesday.

The world's longest frontier has been closed to everything but goods trade since March 21. 

The current shutdown runs out on July 21 and is expected to be extended for a month, said the source, who spoke on condition of anonymity.

The leaders of several Canadian provinces have spoken out against reopening the border as the United States sees an explosion of virus cases in some states.

A few hours after speaking with President Donald Trump on Monday, Canadian Prime Minister Justin Trudeau said a decision would be made in the next few days.

"We recognize that the situation continues to be complex in the United States in regards to COVID-19," Trudeau told reporters.

"Every month, we have been able to extend the border closures to all but essential goods and services and those discussions are ongoing," he added.

A recent poll showed that more than 80 percent of Canadians want the border to stay closed for now.

Half of Americans are in favor of reopening it, compared to just 11 percent of Canadians, according to the Legere poll carried out July 3-5.

The United States is the hardest hit country in the world by the pandemic, with nearly 3.4 million cases and more than 135,000 deaths. 

Canada has recorded more than 8,800 deaths and more than 108,000 cases.

The closure of the US borders with Canada and Mexico has been renewed monthly.

Under normal circumstances, more than 400,000 Americans and Canadians cross their shared frontier each day.