Washington DC - President Donald Trump's administration on Friday lifted tariffs on some Canadian imports after a Republican candidate in a key midterm Senate race said she had lobbied for the change.

The change could help Senator Susan Collins, who faces a strong challenge from a Democrat in the US-Canada border state of Maine, which has been hit hard by Trump's trade war.

She posted on social media that she had "secured" the exemptions for "products crucial to Maine's agricultural industries, including blueberry, potato, apple, and seaweed producers."

The easing of tariffs will also apply to "plywood sheets, some paper products, certain machinery and refrigeration equipment," the White House said in a statement.

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Democrats are targeting Collins' seat in their attempt to win control of Congress from Republicans on November 3.

The economies of the US and Canada are heavily inter-connected, with roughly 70% of all Canadian exports heading to the US.

Tensions between the North American neighbors have been high since trade talks broke down in August, with Trump imposing a slew of new tariffs in response.

Friday's action lifts tariffs on certain goods, but imposes levies on new ones, including carpets, certain valves, and waste products. The new measures will take effect on October 30.

Previous Trump levies on autos, steel, aluminum and lumber have hit Canada hard, forcing job losses and stunting growth. Canada has entered a technical recession this year after two consecutive quarters of economic contraction.

Since taking power in his second term, Trump has upended the global trade order by imposing wide-ranging tariffs on friend and foe alike, saying that other countries have been taking advantage of the US.